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assN o»9S-ioie

OR Research

Volume 30

March 1996

Number 1

Contents

Diagnostic Findings in 132 Great Horned Owls, j. Christian Franson and Susan e.

Little 1

A Retrospective Study of Postmortem Findings in Red-tailed Hawks.

J. Christian Franson, Nancy J. Thomas, Milton R. Smith, Alison H. Robbins, Scott Newman and

Paul C. McCartin 7

Nesting and Food Habits of the Flammulated Owl {Otus flammeolus) in

Southcentral Idaho. Leon R. Powers, Allen Dale, Peter A. Gaede, Chris Rodes, Lance

Nelson, John J. Dean and Jared D. May 15

Breeding, Growth, Development, and Management of the Madagascar

FiSH-EAGLE ( HaLIA fetus VOCIFEROIDES) . Richard T. Watson, Simon Thomsett, Donna
O’Daniel and Richard Lewis 21

Short Communications

The Use of a Power Snare to Capture Breeding Golden Eagles. M.L McGrady and T.R.

Grant 28

A Mechanical Owl as a Trapping Lure for Raptors. Eugene A. Jacobs 31

Feeding of the Bat Falcon {Falco rufigularis) in an Urban Environment. Andres E. Seijas 33

Estimating Age Classes in King Vultures (Sarcoramphus papa) Using Plumage Coloration.

Jack Clinton Eitniear 35

Bigamy in Red-tailed Hawks in Southwestern Yukon. Frank I. Doyle 38

Letters 41

Commentary 46

Book Reviews. Edited by Jeffrey S. Marks 52

Manuscript Referees 56

The Raptor Research Foundation, Inc. gratefully acknowledges a grant and logistical support
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The Journal of Raptor Research (ISSN 0892-1016) is published quarterly and available to individuals for $24.00
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0 This paper meets the requirements of ANSI/NISO Z39.48-1992 (Permanence of Paper).

THE JOURNAL OF RAPTOR RESEARCH

A QUARTERLY PUBLICATION OF THE RAPTOR RESEARCH FOUNDATION, INC.

VoL. 30 March 1996 No. 1

J. Raptor Res. 30(l):l-6

DIAGNOSTIC FINDINGS IN 132 GREAT
HORNED OWLS

J. Christian Franson and Susan E. Little^

U.S. National Biological Service, National Wildlife Health Center, 6006 Schroeder Road,

Madison, WI 53711-6223 U.S.A.

Abstract. — We reviewed diagnostic findings for 132 great horned owl (Bubo virginianus) carcasses that were
submitted to the National Wildlife Health Center from 1975-93. The carcasses were collected in 24 states
but most came from Colorado (N = 21), Missouri (N = 12), Oregon (N = 12), Wyoming {N =11), Illinois
(N = 10), and Wisconsin (N = 9). Forty-two birds were emaciated but presumptive causes of emaciation,
including old injuries, chronic lesions in various organs, and exposure to dieldrin, were found in only 16. A
greater proportion of juveniles (56%) than adults (29%) were emaciated. Twelve owls were shot and 35 died
from other traumatic injuries. Poisonings were diagnosed in 1 1 birds, including five associated with hydrogen
sulfide exposure in oil fields and six cases of agricultural pesticide poisonings. Electrocution killed nine birds
and infectious diseases were found in six. Miscellaneous conditions, including egg impaction, drowning, and
visceral gout were diagnosed in three of the birds and the cause of death was undetermined in 14 owls. While
this review identifies major diagnostic findings in great horned owls, sample bias prevents definitive conclusions
regarding actual proportional causes of mortality.

Key Words: Bubo virginianus; disease', emaciation-, great homed owl', mortality-, toxicosis; trauma.

Encuentros diagnosticos en 132 individuos de la especie Bubo virginianus

Resumen. — Revisamos el diagnostico para 132 carcasas de Bubo virginianus que fueron sometidos al National
Wildlife Health Center desde 1975 a 1993. Las carcasas fueron colectadas en 24 estados, pero la mayoria
venian de Colorado (N = 21), Missouri (N = 12), Oregon (N = 12), Wyoming (N = 11), Illinois (N = 10)
y Wisconsin (N = 9). Cuarenta y dos aves estaban adelgazadas, pero las presuntas causas de adelgazamiento,
incluyendo antiguas heridas, lesiones cronicas en varios organos y exposicidn al dieldren solo fueron encontradas
en 16. El adelgazamiento ocurrio en mayor proporcion en juveniles (56%) que en adultos (297o). Doce buhos
fueron cazados y 35 murieron de otras heridas traumaticas. Envenenamientos se diagnosticaron en 11 aves,
incluyendo cinco asociadas con exposicion a “hydrogen sulfide” en campos petroleros y seis casos de envene-
namiento por perticidas de uso agricola. Nueve aves murieron electrocutadas y en seis se encontro enfermedades
infecciosas. Condiciones miscelaneas, incluyendo impacto de huevos, ahogamiento, fueron diagnosticados en
tres de las aves y causas de muerte no indentificadas ocurrieron en otros 14 individuos. Mientras esta revision
diagnostica los mayores encuentros en B. virginianus, sesgos de la muestra previenen conclusiones definitivas
sobre la proporcionalidad de las causas de muerte.

The great horned owl {Bubo virginianus) is widely
distributed throughout North America and occupies a
greater variety of habitats than any other species of

' Present address: Southeastern Cooperative Wildlife Disease
Study, College of Veterinary Medicine, University of Geor-
gia, Athens, GA 30602 U.S.A.

[Traduccion de Ivan Lazo]

owl (Johnsgard 1988). Great horned owls are adapt-
able feeders with a highly diverse diet that includes
insects, small mammals, and birds (Johnsgard 1988).
Although few data are available regarding the longevity
of wild great horned owls, one band recovery docu-
ments survival for over 20 yr (Klimkiewicz and Futcher
1989). Comparatively little is known about causes of
death in this cosmopolitan species. Scattered reports of

J. Christian Franson and Susan E. Little

VoL. 30, No. 1

great horned owl mortalities exist in reviews of mor-
bidity and mortality of raptors as a group, but com-
pilations of diagnostic findings specific to great horned
owls are lacking. Of the conditions diagnosed in rap-
tors, trauma is among the most frequent and is often
associated with human-related causes (Reran 1981,
Fix and Barrows 1990, Cooper 1993, Franson et al.
1995). Poisonings are also commonly reported causes
of mortality in raptors (Henny et al. 1985, Lumeij et
al. 1993, Franson et al. 1995), and compounds pre-
viously associated with great homed owl deaths include
chlorinated hydrocarbons (Blus et al. 1983a, 1983b,
Stone and Okoniewski 1988, Okoniewski and Novesky
1993) and organophosphorus pesticides (Henny et al.
1987). Little is known about the significance of diseases
in great horned owl populations, although individual
case reports have been published describing several
infectious, parasitic, and neoplastic conditions (Halli-
well 1971, Keymer 1972, Sileo et al. 1975, Kocan et
al. 1977, Clark et al. 1986, Swayne and Weisbrode
1990). We report the results of postmortem exami-
nations of 132 great horned owl carcasses submitted
to the National Wildlife Health Center (NWHC),
Madison, Wisconsin from 1975-93 to provide addi-
tional information on the variety of factors resulting
in morbidity and mortality in this species.

Methods

For this review we selected only intact carcasses, excluding
those that were heavily scavenged, in advanced stages of
decomposition, or cases in which birds had spent extended
periods in rehabilitation. Sp>ecimens, submitted by field bi-
ologists and others from 1975-93, were stored refrigerated
or frozen until examination. Necropsies were conducted by
14 different diagnosticians during the 19-yr period of the
study. Each bird was examined by gross inspection to identify,
for example, abnormalities in organ systems suggestive of
diseases, traumatic injuries indicating gunshot or collisions
with objects, bums suggestive of electrocution, gender, stage
of maturity (juvenile or adult, based on gonadal development),
and to assess the overall body condition. Subsequent labo-
ratory analyses of appropriate tissues were carried out to
identify conditions suggested by necropsy observations. Di-
agnoses of diseases were based on the presence of character-
istic lesions at necropsy and histopathological examination of
tissues or laboratory isolation of the causative agent. We
report the specific causes of death or the most significant
findings identified by the diagnosticians, thus omitting inci-
dental conditions unlikely to have caused harm to the birds.
Proportional categories of findings, according to gender and
age, were compared using the chi-square test for homogeneity
(Daniel 1978).

Brain cholinesterase activity, as an indicator of exposure
to organophosphorus or carbamate pesticides, was determined
for 22 birds using methods described by Ellman et al. (1961)
as modified by Dieter and Ludke (1975) and Hill and Flem-

ing (1982). The magnitude of cholinesterase inhibition was
calculated by comparison with the meem control value (16 ±
2.5 jumoles/min/g) reported by Hill (1988). Pesticide anal-
yses were done at the Patuxent Wildlife Research Center,
Laurel, Msiryland. Organophosphoms and carbamate com-
pounds were recovered from stomach contents by column
extraction and identified by gas chromatography as described
by Belisle and Swineford (1988). Brains were tested for res-
idues of chlorinated hydrocarbons by gas-liquid chromatog-
raphy (Cromartie et al. 1975). Lead and sulfide residues in
tissues were determined according to Boyer (1984) and Feld-
stein (1960), respectively.

Tissues for histopathology were fixed in buffered 10%
formalin, embedded in paraffin, and sectioned for light mi-
croscopy; slides were stained with hematoxylin and eosin for
routine examination, Ziehl-Neelsen acid-fast for mycobac-
teria, or Grocott silver for fungi. Bacterial isolation attempts
were carried out by inoculating tissues onto 5% sheep red
blood agar and eosin-methylene blue plates (DIFCO Lab-
oratories, Detroit, MI U.S.A.), and isolates were character-
ized and identified with the API-20E system (Analytab Prod-
ucts, Plainview, NY U.S.A.). Cell cultures and embryonating
eggs were used for isolation of viruses as described by Doch-
erty and Slota (1988) and Senne (1989).

Results and Discussion

The 132 specimens were submitted from 24 states,
but most came from Colorado {N = 21), Missouri {N
= 12), Oregon (N = 12), Wyoming (N = 11), Illinois
(A^ — 10), and Wisconsin {N = 9). Gender was de-
termined for 121 carcasses (61% were female) and stage
of maturity was assessed for 116 (84% were adults).
Emaciation and trauma were the most frequent di-
agnostic findings followed by gunshot, toxicoses, elec-
trocution, infectious diseases, and miscellaneous (Table
1). No significant findings were reported for 14 (11%)
carcasses. No difference was noted in the distribution
of proportional diagnostic findings between males and
females, but a slight difference (x^ = 12.76, df = 7, P
= 0.08) was indicated when propxirtional categories of
findings for adults were compared with those for ju-
veniles. Emaciation was the primary source of this
difference (x^ = 4.73, df = P = 0.03), and a higher
proportion of juveniles (56%) than adults (29%) were
emaciated.

Emaciation. Although emaciation was diagnosed in
42 (32%) carcasses, factors contributing to this con-
dition were identified in only 16. Two had ocular
lesions (corneal lacerations and plaques), and one had
masses on the eyelids that covered the eyes and may
have impaired sight and hence hunting ability. Lesions
of the eyes are relatively common in raptors, including
great horned owls, and are frequently the result of
some type of physical injury (Murphy et al. 1982).
Joint dislocations and old fractures in various stages

March 1996

Diagnoses in Great Horned Owls

of healing, including one instance of apparent injury
from a leg-hold trap, were found in three carcasses
and probably led to decreased mobility and subsequent
debilitation through malnutrition. Two emaciated owls
had oral lesions, a beak deformity and a proliferative
membranous lesion on the tongue that may have hin-
dered consumption of prey.

Six carcasses had lesions of other organ systems
thought responsible for emaciation, including one car-
cass each with intestinal nematode impaction {Porro-
caecum sp.), abdominal adhesions secondary to a heal-
ing puncture wound, granulomatous hepatitis of un-
determined etiology, and necrotizing verminous pneu-
monia. One carcass had a swollen foot and bacterial
cultures of the foot and liver yielded heavy growth of
Serratia sp., indicating a possible septicemia. Another
bird had a laceration of the skin over the back of the
neck, surrounded by an accumulation of tissue debris,
fly ova, and maggots. This condition was thought to
be antemortem and contributory to emaciation.

Elevated dieldrin residues were found in the brains
of two emaciated owls. An adult female found dead in
Minnesota in 1981 had 2.8 ppm wet weight dieldrin
in its brain. Another adult female, found moribund in
late 1981 in Illinois, had a brain dieldrin concentration
of 4.4 ppm wet weight. Brain residues of 4-5 ppm
wet weight dieldrin are considered to be the lower
threshold of toxicity (Stickel et al. 1969). Although the
use of most organochlorine pesticides is now banned
in the United States, avian mortality continues from
exposure to historically treated areas (Okoniewski and
Novesky 1993), and these compounds should be con-
sidered in cases where emaciated birds are found dead.

For the remaining 26 emaciated owl carcasses, no
etiology was revealed by necropsy or laboratory eval-
uations of tissues. Although heavy parasitism by lice
(Strigiphilus sp.), gastrointestinal parasites {Porrocae-
cum sp. and unidentified capillarids), and renal coccidia
occurred in four of these carcasses, it was concluded
that these infections were secondary to debilitation, not
the cause of it. Liver lead concentrations were deter-
mined for 16 of these birds and in all cases were less
than 2 ppm wet weight, which is considered to be
within normal limits of exposure for many species of
birds (Franson 1996). Brains of two carcasses were
analyzed for organochlorine pesticides, with negative
results. In eight emaciated owls, no testing beyond gross
inspection at necropsy was conducted, precluding any
further diagnosis. These 26 emaciated birds were found
during all months of the year, although slightly more
were found from April to September (N = 15) than

Table 1. Categories of diagnostic findings in 132 great
horned owls.

Diagnostic Finding

Emaciation

Trauma

Undetermined

Gunshot

Toxicoses

Electrocution

Diseases

Miscellaneous®

^ Visceral gout, egg bound, drowning.

Oetober to March (A^ = 11). This may simply reflect
an increased number of observers in the field during
the summer months. Of the 24 birds in this group for
which stage of maturity was determined, eight were
juveniles and 16 were adults. Overall, a greater pro-
portion of juveniles (56%) than adults (29%) were
emaciated. Indeed, most (eight of 10) of the emaciated
juveniles were in this category of unidentified etiology,
suggesting that these birds may have been too naive to
obtain adequate food. These results agree with other
reports, including Cooper (1993) who found a similar
frequency of starvation in barn owls (Tyto alba), and
Ken ward et al. (1993) who reported that juvenile
northern goshawks (Accipiter gentilis) were more fre-
quently diagnosed with starvation than adults.

Trauma. Trauma, excluding gunshot, was the sec-
ond most frequent (26%) finding. Types of trauma
suggested by information provided by the submitter or
lesions observed at necropsy included collision with a
moving vehicle or stationary object, being struck by a
blunt object, and non-gunshot puncture wounds. Ex-
tensive skin and feather damage were noted in eight
owls and skeletal fractures in 17. Hemorrhage, most
frequently of the head, body cavity, and air sacs, was
present in 21 of the 35 trauma cases. Internal organs
including liver, spleen, duodenum, and stomach were
ruptured in six carcasses. Concurrent abnormalities,
including lesions of owl herpesvirus, renal gout, sep-
ticemia, and pododermatitis, were noted in four of the
birds that died from trauma. These findings did not
alter the cause of death as trauma, but may have ren-
dered the owls more susceptible to traumatic injuries.

Gunshot. In 12 (9%) of the carcasses examined,
gunshot wounds were diagnosed based on the presence
of shot in association with fractures, recent hemor-
rhage, and other trauma or when tracts indicating the

J. Christian Franson and Susan E. Little

VoL. 30, No. 1

path of a bullet or pellet could be identified. Seven
were shot with a rifle, three with a shotgun, and two
with an undetermined type of weapon. The frequency
of cases with physical injury as the primary diagnosis
(trauma plus gunshot) was 36%, somewhat less than
the 43% reported in barn owls from England (Cooper
1993).

Toxicoses. Toxicoses were identified in 11 (8%)
great horned owls. Hydrogen sulfide poisoning was
diagnosed in five owls collected in North Dakota oil
fields in 1982. The owls were found near flare or vent
pipes, perhaps used as perches, designed to burn off
or vent natural gases released during crude oil pro-
duction, storage, and pipeline operations (Bicknell
1984). Hydrogen sulfide (1. 5-4.0 ppm wet weight)
was found in pulmonary fluid of each carcass. Hy-
drogen sulfide acts as a direct irritant, producing a
chemical pneumonitis, and combines with and inhibits
metabolic enzymes (Robinson et al. 1990, Short and
Edwards 1989). Inhibition of the central nervous sys-
tem respiratory drive produces apnea, the major cause
of death (Warenycia et al. 1989).

Poisonings by phorate, fenthion, and an unidentified
organophosphorus compound were diagnosed in three
owls. One owl was found dead in South Dakota in
1982 in association with over 275 other dead birds,
primarily ducks. Brain cholinesterase activity in this
bird was inhibited by 83% and phorate (Thimet®)
residues, 200 ppm wet weight, were recovered from
stomach contents that consisted of feathers and grain.
Phorate poisoning was also diagnosed in several of the
ducks, and the owl apparently fed on those carcasses.
Another great horned owl found dead in 1993 in Mis-
souri had a 98% inhibition of brain cholinesterase ac-
tivity and its stomach contents, consisting primarily of
avian remains, contained 14.7 ppm wet weight fen-
thion. Brain cholinesterase activity in a third great
horned owl, found in Utah in 1991, was inhibited by
88% without reversal after incubation of the sample.
These findings are consistent with exposure to an or-
ganophosphorus pesticide (Hill and Fleming 1982,
Smith et al. 1995) but, because the avian remains found
in the stomach were not analyzed, the specific com-
pound was not identified. Secondary poisoning by or-
ganophosphorus compounds, including fenthion, has
been previously reported in several species of raptors
(Henny et al. 1985, 1987, Bruggers et al. 1989, Hunt
et al. 1991).

The brain cholinesterase activity of an owl found
dead in Delaware in 1989 was within the normal
range, but carbofuran (4.6 ppm wet weight) was re-

covered from the feathers and flesh found in its stom-
ach. The carcass was partially decomposed and the
lack of cholinesterase inhibition was probably the result
of postmortem reactivation of the enzyme (Hill and
Fleming 1982), one of the factors that contribute to a
lack of correlation between cholinesterase inhibition
and carbamate exposure (Greig- Smith 1991). Two
birds died of poisoning by chlorinated hydrocarbons
(endrin and chlordane) and those cases are described
elsewhere (Blus et al. 1983a, 1983b).

Electrocution. Nine (7%) great horned owls died
of electrocution, including three from Colorado, two
from Oregon, two from Illinois, and one each from
Arkansas and Wisconsin. The frequency of electro-
cution in this group of owls is considerably lower than
the rates of 12% and 25% reported for bald eagles
{Haliaeetus leucocephalus) and golden eagles (Aquila
chrysaetos), respectively (Franson et al. 1995),

Infectious Diseases. Infectious diseases were di-
agnosed in six (4%) of the great homed owls. Two
owls found dead in Nebraska in 1992 had gross and
microscopic lesions consistent with owl herpesvirus in-
fection (Green and Shillinger 1936, Sileo et al. 1975).
Nodular lesions characteristic of avian tuberculosis were
found in the liver and spleen of an owl collected in
Nevada in 1984 and one found in Nebraska in 1987.
Acid-fast bacteria, consistent with tuberculosis, were
seen microscopically in impression smears of tissues
and Mycobacterium avium was isolated from the liver
of both birds. Bacterial pneumonia was diagnosed his-
tologically in an owl found in 1980 in Oregon, but
bacterial cultures of lung were negative. In 1980 an
owl from Wisconsin was found to have numerous small
abscesses in its enlarged liver and spleen and bacterial
culture of spleen yielded heavy growth of Staphylococ-
cus aureus.

Miscellaneous. Unusual diagnoses were reached in
three of the 132 cases reviewed. One adult female had
extensive bruising and tissue damage surrounding a
fully formed egg in the distal oviduct, and apparently
was egg bound. Drowning was diagnosed upon dis-
covering water in the anterior thoracic air sacs of an-
other owl. Severe visceral gout characterized by urate
deposits within the kidneys and throughout the intes-
tinal tract was found in a third owl.

Cause of death was not determined in 14 (11%) of
the great horned owl carcasses examined. All of the
carcasses included in this category were found to have
adequate stores of body fat and no evidence of trauma.
In five of the birds, no testing beyond gross inspection
at necropsy was conducted. Liver lead concentrations

March 1996

Diagnoses in Great Horned Owls

were determined in five cases and brain cholinesterase
activities were evaluated in two of the 14 birds, but
those results were within normal limits. Isolation of
infectious agents was attempted in six of the 14 cases,
hut proved unsuccessful.

The significance of these results and their impact
on great horned owl populations are difficult to eval-
uate because of the retrospective nature of the study
and the nonrandom carcass collection techniques.
However, this report does serve to identify major di-
agnostic findings in great horned owls. Increasing ed-
ucational efforts may help mitigate causes of mortality
related to human activities. More judicious use and
monitoring of pesticides should help prevent poisonings
and modifications to structures such as power lines and
utility poles may reduce electrocution and trauma mor-
talities. Emaciation of undetermined etiology is a sig-
nificant finding and should be further evaluated. A
study designed to examine emaciation in great horned
owls with regard to age, food availability, and the
temporal and geographic distribution of emaciated birds
may help to identify potential causes of emaciation.

Acknowledgments

We thank the many field biologists who submitted these
specimens amd the members of the Resource Health Team
of the National Wildlife Health Center for consulting with
field personnel. Those who conducted the necropsies included

C. Brand, K. Converse, S. Kerr, J. Langenberg, L. Locke,
H. McAllister, C. Meteyer, S. Schmeling, L. Sileo, R. Stroud,
and N. Thomas. Results of testing for microbiology, virology,
toxicology, and parasitology were provided by R. Duncan,

D. Docherty, M. Smith, B. Campbell, R. Cole, and B. Tug-
gle. Chemists at the Patuxent Wildlife Research Center and
the Wisconsin Central Animal Health Laboratory conducted
pesticide and sulfide analyses, respectively. C. Thoen and G.
Colgrove of the National Veterinary Services Laboratories
identified the mycobacteria. M. Samuel provided statistical
interpretation. L. Blus, W. Davidson, J. Fischer, C. Henny,
L. Locke, and V. Nettles and an anonymous reviewer pro-
vided helpful comments on the manuscript.

Literature Cited

Belisle, a. a. and D.M. Swineford. 1988. Simple, spe-
cific analysis of organophosphorus and carbamate pesti-
cides in sediments using column extraction and gas chro-
matography. Environ. Toxicol. Chem. 7:749-752.

Blus, L.J., C.J. Henny, T.E. Kaiser and R.A. Grove.
1983a. Effects on wildlife from use of endrin in Wash-
ington state orchards. Trans. N. Am. Wildl. Nat. Resour.
ConJ. 48:159-174.

, O.H. Pattee, C.J. Henny and R.M. Prouty.

1983b. First records of chlordane-related mortality in
wild birds. J. Wildl. Manage. 47:196-198.

Bicknell, W.B. 1984. A cooperative hydrogen-sulfide
monitoring study, the Lone Butte oil field, McKenzie

County, North Dakota. USDI Fish Wildl. Serv., Unpubl
Rep., Bismarck, ND U.S.A.

Boyer, K.W. 1984. Metals and other elements at trace
levels in foods. Pages 444-476 in S. Williams [Ed.], Of-
ficial methods of analysis of the Association of Official
Analytical Chemists. Association of Official Analytical
Chemists, Inc., Arlington, VA U.S.A.

Bruggers, R.L., M.M. Jaeger, J.O. Keith, P.L. Hegdal,
J.B. Bourassa, a. a. Latigo and J.H. Gillis. 1989.
Impact of fenthion on nontarget birds during quelea con-
trol in Kenya. Wildl. Soc. Bull. 17:149-160.

Clark, F.D., A.D. Chinnah and S.A. Garner. 1986.
Aspergillosis in a great homed owl {Bubo virginianus): a
case report. Southwest. Vet. 37:11-12.

Cooper, J.E. 1993. Pathological studies on the barn owl.
Pages 34-37 in P.T. Redig, J.E. Cooper, J.D. Remple,
D.B. Hunter and T. Hahn [Eds.], Raptor biomedicine.
Univ. Minnesota Press, Minneapolis, MN U.S.A.
Cromartie, E., W.L. Reichel, L.N. Locke, A. A. Belisle,
T.E. Kaiser, T.G. Lamont, B.M. Mulhern, R.M.
Prouty and D.M. Swineford. 1975. Residues of or-
ganochlorine pesticides and polychlorinated biphenyls and
autopsy data for bald eagles, 1971-72. Pestic. Monit. J. 9:
11-14.

Daniel, W.W. 1978. Applied nonparametric statistics.

Houghton Mifflin Co., Boston, MA U.S.A.

Dieter, M.P. and J.L. Ludke. 1 975. Studies on combined
effects of organophosphates and heavy metals in birds. I.
Plasma and brain cholinesterase in coturnix quail fed
methyl mercury and orally dosed with parathion. Bull.
Environ. Contam. Toxicol. 13:257-262.

Docherty, D.E. and P.G. Slota. 1988. Use of muscovy
duck embryo fibroblasts for the isolation of viruses from
wild birds. /. Tiss. Cult. Meth. 11:165-170.

Ellman, G.L., K.D. Courtney, V. Andres, Jr- AND R.M.
Featherstone. 1961. A new and rapid colorimetric
determination of acetylcholinesterase activity. Biochem.
Pharmacol. 7:88-95.

Feldstein, M. 1960. Microdiffusion analysis as applied
to toxicology. Pages 639-659 in C.P. Stewart and A.
Stolman [Eds.], Toxicology — mechanisms and analytical
methods. Vol. I. Academic Press, New York, NY U.S.A.
Fix, A.S. and S.Z. Barrows. 1990. Raptors rehabilitated
in Iowa during 1986 and 1987: a retrospective study. /.
Wildl. Dis. 26:18-21.

Franson, J.C. 1996. Interpretation of tissue lead residues
in birds other than waterfowl. In W.N. Beyer, G.H.
Heinz and A.W. Redmon [Eds.], Environmental contam-
inants in wildlife: interpreting tissue concentrations. Lew-
is Publishers, Boca Raton, FL U.S.A. In press.

, L. Sileo and N.J. Thomas. 1995. Causes of

eagle deaths. Page 68 in E.T. LaRoe, G.S. Farris, C.E.
Puckett, P.D. Doran and M.J. Mac [Eds.], Our living
resources: a report to the nation on the distribution, abun-
dance, and health of U.S. plants, animals, and ecosystems.
USDI, Natl. Biol. Serv., Washington, DC U.S.A.

J. Christian Franson and Susan E. Little

VoL. 30, No. 1

Green, R.G. and J.E. Shillinger. 1936. A virus disease
of owls. Am. J. Pathol. 12:405-410.

Greig-Smith, P.W. 1991. Use of cholinesterase measure-
ments in surveillance of wildlife poisoning in farmland.
Pages 127-150 in P. Mineau [Ed.], Cholinesterase-in-
hibiting insecticides; their impact on wildlife and the en-
vironment. Vol. 2, Elsevier, Amsterdam, The Nether-
lands.

Haluwell, W.H. 1971. Lesions of Marek’s disease in a
great homed owl. Avian Dis. 15:49-55.

Henny, C.J., L.J. Blus, E.J. Kolbe and R.E. Fitzner.
1985. Organophosphate insecticide (famphur) topically
applied to cattle kills magpies and hawks. /. Wildl. Man-
age. 49:648-658.

, E.J. Kolbe, E.F. Hill AND L.J. Blus. 1987. Case

histories of bald eagles and other raptors killed by or-
ganophosphoms insecticides topically applied to livestock.
/. Wildl. Dis. 23:292-295.

Hill, E.F. 1988. Brain cholinesterase activity of apparently
normal wild birds. J. Wildl. Dis. 24:51-61.

AND W.J. Fleming. 1982. Anticholinesterase poi-
soning of birds: field monitoring and diagnosis of acute
poisoning. Environ. Toxicol. Chem. 1:27-38.

Hunt, K.A., D.M. Bird, P. Mineau and L. Shutt. 1991.
Secondary poisoning hazatrd of fenthion to American kes-
trels. Arch. Environ. Contam. Toxicol. 21:84-90.

JOHNSGARD, P.A. 1988. North American owls. Smithson-
ian Inst. Press, Washington, DC U.S.A.

Kenward, R.E., V. Marcstrom and M. Karlbom. 1993.
Causes of death in radio-tagged northern goshawks. Pages
57-61 in P.T. Redig, J.E. Cooper, J.D. Remple, D.B.
Hunter and T. Hahn [Eds.], Raptor biomedicine. Univ.
Minnesota Press, Minneapolis, MN U.S.A.

Reran, D. 1981. The incidence of man-caused and natural
mortalities to raptors. Raptor. Res. 15:108-112.

Keymer, I.F. 1972. Diseases of birds of prey. Vet. Rec. 90:
579-594.

Klimkiewicz, M.K. and A.G. Futcher. 1989. Longevity
records of North American birds — supplement 1 . /. Field
Omithol. 60:469-494.

Kogan, A. A., J. Snelling and E.C. Greiner. 1977. Some
infectious md parasitic diseases in Oklahoma raptors. /.
Wildl. Dis. 13:304-306.

Lumeij, J.T., I. Westerhof, T. Smit and T.J. Spier-
ENBURG. 1993. Diagnosis and treatment of poisoning
in raptors from the Netherlands; clinical case reports and
review of 2,750 postmortem cases, 1975-1988. Pages 233-
238 in P.T. Redig, J.E. Cooper, J.D. Remple, D.B.
Hunter and T. Hahn [Eds.], Raptor biomedicine. Univ.
Minnesota Press, Minneapolis, MN U.S.A.

Murphy, C.J., T.J. Kern, K. McKeever, L. McKeever
AND D. MacCoy. 1982. Ocular lesions in free-living
raptors. J. Am. Vet. Med. Assoc. 181:1302-1304,

Okoniewski, J.C. AND E. Novesky. 1993. Bird poisonings
with cyclodienes in suburbia: links to historic use on turf.
/. Wildl. Manage. 57:630-639.

Robinson, F.R., L.J. Runnels, D.A. Conrad, R.F. Te-
CLAW and H.L. Thacker. 1990. Pathologic response
of the lung to irritant gases. Vet. Human Toxicol. 32:569-
572.

Senne, D.A. 1989. Vims propagation in embryonating
eggs. Pages 176-181 in H.G. Purchase, L.H. Arp, C.H.
Domermuth and J.E. Pearson [Eds.], A laboratory man-
ual for the isolation and identification of avian pathogens.
Kendall/Hunt Publ. Co., Dubuque, lA U.S.A.

Short, S.B. and W.C. Edwards. 1989. Sulfur (hydrogen
sulfide) toxicosis in cattle. Vet. Human Toxicol. 31:451-
453.

SiLEO, L., H.C. Carlson and S.C. Crumley. 1975. In-
clusion body disease in a great horned owl. J. Wildl. Dis
11:92-96.

Smith, M.R., N.J. Thomas and C. Hulse. 1995. Ap-
plication of brain cholinesterase reactivation to differen-
tiate between organophosphoms and carbamate pesticide
exposure in wild birds. J. Wildl. Dis. 31:263-267.

Stickel, W.H., L.F. Stickel and J.W. Spann. 1969. Tis-
sue residues of dieldrin in relation to mortality in birds
and mammals. Pages 174-204 in M.W. Miller and G.G.
Berg [Eds.], Chemical fallout — current research on per-
sistent pesticides. Charles C Thomas, Springfield, IL
U.S.A.

Stone, W.B. and J.C. Okoniewski. 1988. Organochlorine
pesticide-related mortalities of raptors and other birds in
New York, 1982-1986. Pages 429-438 in T.J. Cade,
J.H. Enderson, C.G. Thelander and C.M. White [Eds.],
Peregrine falcon populations: their management and re-
covery. Peregrine Fund, Inc., Boise, ID U.S.A.

Swayne, D.E. and S.E. Weisbrode. 1990. Cutaneous
mast cell tumor in a great horned owl (Bubo virginianus).
Vet. Pathol. 27:124-126.

Warenycia, M.W., L.R. Goodwin, C.G. Benishin, R.J.
Reiffenstein, D.M. Francom, J.D. Taylor and F.P.
Dieken. 1989. Acute hydrogen sulfide poisoning —
demonstration of selective uptake of sulfide by the brain-
stem by measurement of brain sulfide levels. Biochem.
Pharmacol. 38:973-981.

Received 7 June 1995; accepted 1 September 1995

/. Raptor Res. 30(1):7-14
© 1996 The Raptor Research Foundation, Inc.

A RETROSPECTIVE STUDY OF POSTMORTEM
FINDINGS IN RED-TAILED HAWKS

J. Christian Franson, Nancy J. Thomas, Milton R. Smith,
Alison H. Robbins,^ Scott Newman^ and Paul C. McCartin^

U.S. National Biological Service, National Wildlife Health Center, 6006 Schroeder Road,

Madison, WI 53711-6223 U.S. A.

Abstract. — We studied necropsy results from carcasses of 163 red-tailed hawks (Buteo jamaicensts)
submitted to the National Wildlife Health Center from 1975 through 1992. The most frequent post-
mortem finding was emaciation of unknown etiology, diagnosed in 33 (20%) carcasses. Proportionally
more juveniles than adults were emaciated. Evidence of non-gunshot trauma, often suggestive of collision
with vehicles or structures near roadways, was found in 29 (18%) birds. Of 25 (15%) toxicoses, 20 were
attributed to agricultural pesticides, including famphur (4), fenthion (3), carbofuran (2), phosphamidon
(2), endrin (1), and unidentified organophosphorus compounds (8). Lead and strychnine poisoning were
diagnosed in two birds each, and selenium poisoning in one. Diseases, including aspergillosis, tuberculosis,
pasteurellosis, and pox, were found in 21 (13%) hawks. Gunshot and electrocution were each diagnosed
in six (4%) birds, one (0.6%) was trapped, miscellaneous conditions were found in 10 (6%), and no
diagnosis could be determined for 32 (19%) of the carcasses.

Key Words: Buteo jamaicensis; diseases-, mortality, pesticides-, poisoning-, red-tailed hawk-, trauma.

Un estudio retrospectivo de encuentros postmortem en Buteo jamaicensis

Resumen. — Estudiamos los resultados de la necropsia de restos de 163 individuos de la especie Buteo
jamaicensis sometidos al National Wildlife Health Center desde 1975 hasta 1992. El encuentro post-
mortem mas frecuente fue adelgazamiento de etiologia desconocida, diagnosticado en 33 (20%) restos.
Proporcionalmente, mas juveniles que adultos estaban adelgazados. Traumas no causados por armas de
fuego, sino que por posibles colisiones con vehiculos o estructuras cerca de las carreteras, fueron encontrados
en 29 (18%) aves. De 25 (15%) individuos intoxicados, 20 fueron atribuidos a pesticidas de uso agricola,
incluyendo “famphur” (4), “fenthion” (3), “carbofuran” (2), “phosphamidon” (2), “endrin” (1) y com-
puestos organofosforados no identificados (8). Envenenamiento por plomo y estricnina fueron diagnos-
ticados en dos aves, respectivamente, envenenamiento por selenio, solo en una. Enfermedades, incluyendo
aspergilosis, tuberculosis, pasteurelosis y viruela, fueron encontradas en 21 individuos (13%). Disparos
y electrocucion como causa de muerte fue diagnosticada en seis aves (4%), una fue atrapada, condiciones
miscelaneas fueron encontradas en 10 (6%). No se pudo emitir un diagnostico para 32 (19%) restos.

[Traduccion de Ivan Lazo]

The red-tailed hawk {Buteo jamaicensis) is a fre-
quent breeder in North America and the most abun-
dant hawk in the United States and southern Canada
during cold-weather months (Johnsgard 1990). De-
spite its wide range and abundance, little is known
about factors that influence the health of the red-
tailed hawk. Occasional case reports of diagnostic

Present addresses: ’Wildlife Clinic, Tufts University, School
of Veterinary Medicine, 200 Westboro Road, North Graf-
ton, MA 01536 U.S. A.; ^Wildlife Health Center, School
of Veterinary Medicine, University of California, Davis,
C A 95616 U.S. A.; ^New England Wildlife Center, 1 9 Fort
Hill Street, Hingham, MA 02043 U.S.A.

findings, primarily infectious diseases and toxicoses,
have been published but most of these accounts in-
volve only one or several birds. Some of the diseases
previously reported from individual sick and dead
red-tailed hawks include avian pox (Halliwell 1972,
Fitzner et al. 1985, Chubb 1987, Rosskopf et al.
1987,), tuberculosis (Sykes 1982, Mollhofif 1983,
Clark 1986), erysipelas (Pace et al. 1987), and oral
capillariasis (Santiago et al. 1985). Poisonings doc-
umented in red-tailed hawks have often been the
result of their exposure to pest-control chemicals.
Henny et al. (1985, 1987) reported mortality in red-
tailed hawks from exposure to famphur, an insec-
ticide topically applied to livestock for parasite con-
trol, and Hooper et al. (1989) described intoxication

Franson et al.

VoL. 30, No. 1

Table 1. Postmortem findings in 163 red-tailed hawks.

Category

Emaciation

Undetermined^

Trauma

Toxicoses

Diseases

Miscellaneous*’

Gunshot

Electrocution

Trapped

® Postmortem examination revealed no cause of death or significant
findings.

Peritonitis, visceral gout, parasitism, hepatitis, endocarditis, and
other nonspecific infections based on gross observations only, eti-
ologies unknown.

of red-tailed hawks by organophosphorus pesticides
applied to orchards. Cyclodiene organochlorine in-
secticides persistent in soil in urban and suburban
areas have been implicated in recent poisonings of
red-tailed hawks (Okoniewski and Novesky 1993).

In an effort to evaluate the scope of the causes of
illness and death in red-tailed hawks, we studied
diagnostic findings from 163 carcasses examined at
the National Wildlife Health Center (NWHC) over
nearly 20 yr. Because of the nonrandom nature of
carcass collection and submission, this summary does
not necessarily reflect the actual proportional dis-
tribution of causes of illness and mortality in the
red-tailed hawk population as a whole. However,
our findings identify some of the major factors that
cause or contribute to the death of these hawks.

Methods

We reviewed and summarized records of 163 red-tailed
hawk carcasses that were submitted for cause of death
determination to the NWHC, a U.S. Department of In-
terior facility that provides diagnostic services to natural
resource managers throughout the United States and its
territories. Most of these birds had been found dead in the
field and were collected in 26 states from 1975 through
1992. Some birds were captured alive and later died or
were euthanized because of the extent of their injuries or
illness at the time of capture, but no birds undergoing
extended rehabilitation were included in the review. A
gross examination, including a description of wounds and
abnormalities and an evaluation of overall body condition
with respect to fat reserves and pectoral muscular devel-
opment, was conducted on each carcass. Samples of organs
were tested for a variety of microorganisms, parasites, and
toxins as indicated by gross findings and field information
provided by the collector. Tissues for histopathology were
fixed in 10% buffered formalin, embedded in paraffin.

sectioned for light microscopy and stained with hematox-
ylin and eosin for routine examination, Ziehl-Neelsen acid-
fast for mycobacteria, and/or Grocott silver for fungi. Bac-
teria were isolated by inoculation of tissues onto 5% sheep
red-blood agar and eosin-methylene blue plates (DIFCO
Laboratories, Detroit, MI U.S.A.), incubated at 37° C for
72 hr, and then characterized with the API-20E system
(Analytab Products, Plainview, NY U.S. A.). Tissues for
virus isolation attempts were processed according to Doch-
erty and Slota (1988) and Senne (1989).

When agricultural pesticide poisoning was suspected by
those who submitted the carcasses, or when the pathologist
found stomach contents of animal remains consistent with
possible secondary poisoning, brains were screened for
cholinesterase activity. Cholinesterase assays were accord-
ing to Ellman et al. (1961) and as later modified by Dieter
and Ludke (1975) and Hill and Fleming (1982), including
incubation (18 hr at 37°C) and retesting of samples with
initially low enzyme activities. Cholinesterase inhibition
was calculated by comparison with normal published val-
ues (Hill 1988) or control values determined by the NWHC
(Smith et al. 1995). In most cases where inhibition of brain
cholinesterase activity was noted, stomach contents were
analyzed at the Patuxent Wildlife Research Center, Lau-
rel, Maryland for 24 organophosphorus and six carbamate
compounds according to Belisle and Swineford (1988) (Pa-
tuxent Analytical Control Facility standard operating pro-
cedure 0-25.00). Brains were analyzed for residues of
chlorinated hydrocarbons by gas-liquid chromatography
(Cromartie et al. 1975, Blus et al. 1989), liver lead residues
were determined according to Boyer (1984), and methods
for selenium analysis of liver followed Krynitsky (1987).
Analysis of stomach contents for strychnine was according
to Feldstein (1960). Animal material found in esophagi
and stomachs of the hawks were described, but not iden-
tified to species. Chi-square and analysis of variance (Zar
1984) were used for age and gender comparisons of di-
agnostic findings.

Results and Discussion

General Findings. Ninety-seven (60%) of the 163
red-tailed hawks were females, 59 (36%) were males,
and seven (4%) were of undetermined gender. The
age distribution was 83 (51%) juveniles, 74 (45%)
adults, and 6 (4%) undetermined. The gender dis-
tribution by age, of the 155 birds for which both
were determined, was 51 juvenile females, 31 ju-
venile males, 46 adult females, and 27 adult males.
The most frequent state of origin was California {N
= 54, 33%), followed by Wisconsin (N = 27, 16%)
and Illinois (N = 17, 10%). Factors contributing to
or directly causing the death of the bird were deter-
mined for 131 carcasses. The most frequent findings
were emaciation, trauma, toxicoses, and diseases
(Table 1). Less common causes of death included
gunshot, electrocution, trapping, and a variety of
miscellaneous conditions. We found no differences
in the proportional distribution of gender or age

March 1996

Postmortems of Red-tailed Hawks

among the various categories of diagnostic findings.
However, there was a significant (x^ = 5.26, df =
1 , P = 0.02) difference in the distribution of juveniles
and adults when emaciated birds were compared
with all other groups combined. Proportionally more
juveniles than adults were emaciated.

Because a diagnosis of emaciation was applied
subjectively, based on visual observation of fat re-
serves and muscle mass, we sought to verify this
determination by comparing the mass of emaciated
red-tailed hawks with the mass of birds diagnosed
with gunshot, other trauma, and electrocution. The
latter three groups were selected for comparison be-
cause we expected hawks that died such acute deaths
would have body mass representative of the normal
population. In fact, the mass of birds in this acute
death group (Table 2) agreed closely with those
reported by Dunning (1984). Regardless of gender
or age, the average mass of emaciated birds was
significantly {F = 78.21, df = 1,46, P = 0.0001) less
than birds in other mortality categories (Table 2).

Emaciation. Diagnosed in 33 birds, emaciation
was the most frequent finding, but examination of
the carcasses failed to reveal its causes in individual
birds or an explanation for the high rate of occur-
rence. These hawks may have died of starvation
because of scarcity of prey or perhaps had unap-
parent injuries or diseases that led to their emaciated
condition. However, chronic poisonings cannot be
ruled out because tissues were not analyzed for the
presence of toxins. As for the finding that more ju-
veniles than adults suffered from emaciation, we
speculate that juveniles, because of their more re-
stricted diet (Craighead and Craighead 1956), may
be less successful in obtaining food during periods
of adverse environmental conditions, reduced prey
populations, or dispersal into new territories.

Trauma. Trauma, exclusive of gunshot, was the
second most commonly identified finding and was
noted in 29 red-tailed hawk carcasses. Frequent
traumatic injuries included fractures of long bones,
vertebrae, and of the skull. These injuries and the
evaluation of information, when provided, regarding
the locations where the carcasses were found sug-
gested that at least 1 0 of these birds probably collided
with vehicles or structures near roadways. The fact
that human observers spend a great deal of time on
or near roadways may have contributed to the high
frequeney of traumatic injuries found among the
hawks that were submitted.

Gunshot trauma was diagnosed in six birds. The

Table 2. Mass (g) of emaciated red-tailed hawks and of
those that died acute deaths.

Mean Mass (SD, N)

Sex

Emaciation

Acute Death®

Male

Adult

680 (94, 6)t>

1031 (72, 4)

Juvenile

747 (118, 7)

1025 (167, 3)

Female

Adult

1040 (85, 2)

1236 (173, 11)

Juvenile

777 (105, 12)

1192 (131, 9)

® Trauma, gunshot, and electrocution.

^ Regardless of sex or age, weights of emaciated hawks were sig-
nificantly {F = 78.21, df = 1,46, P = 0.0001) less than weights of
birds in the acute death category.

appearance of the wounds and characteristics of pro-
jectiles, or portions thereof, that were recovered led
pathologists to conclude that four of the hawks were
shot with rifles and two with shotguns.

Toxicoses. Of the 25 poisoning cases in red-tailed
hawks, 20 were attributed to agricultural pesticides.
A single case of poisoning by endrin, a chlorinated
hydrocarbon pesticide, was diagnosed in a bird of
very poor body condition collected in 1982. This
hawk was among 11 species of Falconiformes that
died of endrin poisoning in or near orehards in cen-
tral Washington (Blus et al. 1989). Organophos-
phorus or carbamate compounds were responsible
for the remaining 19 agricultural chemical poison-
ings, collected from 1987 through 1992, based on
brain cholinesterase activity or analytical identifi-
cation of a pesticide in stomach contents. Carbo-
furan, phosphamidon, fenthion, and famphur were
responsible for 1 1 of the mortalities (Table 3). Stom-
ach contents in 10 of these hawks were of avian
origin and the other contained the remains of a small
mammal, consistent with secondary pesticide poi-
soning from consuming intoxicated prey (Stone et
al. 1984, Henny et al. 1985, 1987, Hunt et al. 1992).
Brain cholinesterase activity was inhibited by 77-
97%, except for one case of carbofuran poisoning in
which the initial activity was inhibited by only 39%,
probably because of partial postmortem reactivation
(Hill and Fleming 1982). After incubation and re-
testing, the cholinesterase activity of this sample in-
creased to 113% of normal, a characteristic response
to carbamate exposure (Smith et al. 1995) and the
carbofuran concentration in stomach contents was

Franson et al.

VoL. 30, No. 1

Table 3. Organophosphorus and carbamate pesticide
poisonings in 11 red-tailed hawks.

Pesticide

State
Year {N)

CoNCEN- Brain
TRATION IN ChE*’
Stomach Inhibi-
Gontents® tion (%)

Carbofuran

MD, 1988 (1)

150

MD, 1988 (1)

Phosphamidon

KS, 1990 (2)

3.5, 9.7

94, 97

Fenthion

IL, 1992 (2)

0.5, 2.8

83, 87

MO, 1992 (1)

Famphur

UT, 1987 (1)

0.2

UT, 1991 (2)

0.9, 0.5

78, 77

WA, 1989 (1)

1.5

^ ppm, wet weight; stomach contents consisted of avian remains in
all instances, except that parts of a small mammal were found in
the first carbofuran (150 ppm) case listed.

Cholinesterase.

150 ppm wet weight. The relatively low level of
brain cholinesterase inhibition, but high carbofuran
residues, are in agreement with Greig-Smith (1991)
who reported that a correlation between brain cho-
linesterase activity and carbamate pesticide residues
is lacking.

In eight birds, brain cholinesterase activity was
inhibited by 48-99%, without reversal after incu-
bation of the sample, but chemical analysis of stom-
ach contents was not done (N = 5) or failed to reveal
the presence of any of the compounds included in
the assay (N = 3). The magnitude of cholinesterase
inhibition and the lack of reversal is consistent with
exposure to an organophosphorus compound (Ludke
et al. 1975, Hill and Fleming 1982, Smith et al.
1995), and we describe these as cases of suspected
poisoning by an organophosphorus compound. In
fact, three of these birds were found during mortality
events where stomach contents from other red-tailed
hawks were positive for famphur or phosphamidon.
At least three possible explanations exist for the
situation in which brain cholinesterase results and
field circumstances point to organophosphate poi-
soning, but analytical results from stomach contents
are negative: (1) Brain cholinesterase activity can
remain inhibited several days after exposure to or-
ganophosphorus pesticides (Fleming and Bradbury
1981), and it is possible that by the time these birds
died the concentration of the responsible chemical in
stomach contents was below detectable limits as a
result of degradation, absorption, or regurgitation;

(2) A loss of brain cholinesterase activity might result
from advanced decomposition, although Prijono and
Leighton (1991) found this enzyme to be quite stable
for up to 8 d at 25°C; or, (3) The birds may have
been poisoned by a compound not included in the
testing procedure.

The earliest of the organophosphorus and car-
bamate poisonings in this group of birds occurred
in 1987, well after secondary famphur poisoning was
documented in a red-tailed hawk in 1982 (Henny
et al. 1985). This may reflect nonrandom sample
bias, expressed by an increased interest in these types
of poisonings during the mid-1980s, and the fact
that screening for brain cholinesterase activity was
not common practice at the National Wildlife Health
Center until about 1985. Our finding of a 12% (19
of 163) frequency of organophosphorus and carba-
mate poisonings in red-tailed hawks is similar to
that (17%) reported in a 1975-88 survey in The
Netherlands of eight raptor species (Lumeij et al.
1993), but higher than that found in some other
studies. A 30-yr summary of over 4300 bald eagle
{Haliaeetus leucocephalus) and golden eagle (Aquila
chrysaetos) mortalities that began in the early 1960s
indicated an overall frequency of anticholinesterase
poisonings of about 3% (Franson et al. 1995). Most
of those cases occurred after the early 1980s. Grem-
illion-Smith and Woolf (1993) tested brain cholin-
esterase activity of 1 05 raptor carcasses of five species
collected in Illinois in 1985-87, and reported that
6% were anticholinesterase poisoning suspects.

Lead toxicosis was diagnosed in one red-tailed
hawk collected in Illinois in 1981 and one found in
California in 1985. Both birds were emaciated and
the liver-lead concentrations were 4.3 and 10 ppm
wet weight, respectively, but no ingested lead was
found. In raptors, liver-lead residues of 2-4 ppm
wet weight indicate unusual exposure to lead, while
residues greater than 5 ppm wet weight are com-
patible with death when pathology consistent with
lead poisoning is present (Franson 1996). The liver-
lead concentration of 4.3 ppm wet weight in the first
hawk reflects lead exposure in the toxic range but,
because emaciation was the only lesion noted, this
concentration is not itself conclusive for a definitive
diagnosis of fatal lead poisoning. We can merely
infer that this bird was affected by lead toxicosis.
The liver-lead concentration of 10 ppm wet weight
and the emaciated condition of the second hawk are
compatible with a lead-poisoning diagnosis. This
second case is complicated by the presence of pas-

March 1996

Postmortems of Red-tailed Hawks

teurellosis {Pasteurella multocida) and aspergillosis
{Aspergillus jumigatus) in the bird’s respiratory tract.
Debilitation and immunosuppression, subsequent to
lead exposure, may have facilitated the invasion of
these organisms. Immunosuppressive efTects of lead
are well-known from studies of laboratory animals
but less understood in wildlife (Franson 1986),
although reduced numbers of immunologic cells in
mallards {Anas platyrhynchos) exposed to lead has
been reported (Rocke and Samuel 1991).

One hawk found in Minnesota in 1983 and an-
other in California in 1990 died of strychnine poi-
soning, with concentrations of strychnine in stomach
contents of 16 and 330 ppm wet weight, respectively.
The death of a hawk collected in 1987, from an area
in California with a previous history of selenium
contamination (Ohlendorf et al. 1990, Schuler et al.
1990), was attributed to selenium toxicosis. The car-
cass was emaciated and had selenium residues of 1 9
ppm wet weight in its liver. Background residues of
selenium in avian liver are generally less than about
5 ppm wet weight (White et al. 1980, Hutton 1981).
Mallard ducklings that died after experimental se-
lenium exposure had liver selenium residues of 7
and 18 ppm wet weight (Heinz et al. 1988). Eastern
screech-owls {Otus asio) euthanized after receiving
selenomethionine in their diet for more than 3 mo
were thin and had a mean liver selenium concen-
tration of 17 ppm wet weight (S.N. Wiemeyer pers.
comm.).

Diseases. Evidence of infectious disease was the
primary finding in 21 of the red-tailed hawk car-
casses. Aspergillosis was the most frequent of these,
occurring in nine birds. Gross observations were
consistent with chronic disease, characterized by the
presence of fungal mats, caseous nodules, or plaques
within the respiratory system, and Aspergillus fu-
migatus was isolated from tissues. Aspergillosis is
frequently associated with other conditions that
weaken birds and predispose them to infection
(O’Meara and Witter 1971). Concurrent diseases,
two cases of pasteurellosis and one of mycobacteriosis
{Mycobacterium sp.) were found in three of these
hawks, but no other infectious agents or contributory
causes were identified in the other six birds with
aspergillosis. Aspergillosis is also common in birds
undergoing rehabilitation, but four of the hawks
were found dead in the field and the others were in
captivity for less than 7 d.

Pasteurellosis was found in five of these red-tailed
hawks, including two cases where it was the primary

finding, one case associated with lead poisoning and
aspergillosis, and two concurrent with aspergillosis
only. Of the two birds with primary pasteurellosis,
one had a swollen foot and yellow fibrinous material
in the pericardial sac, both of which yielded cultures
of P. multocida. The only lesion seen in the second
hawk was congestion of the lungs, but P. multocida
was isolated from liver, lung, and heart. No lesions
suggestive of pasteurellosis were seen in the lead-
poisoned hawk, but P. multocida was isolated from
air sacs. Gross lesions in the birds with concurrent
aspergillosis/pasteurellosis included thickened air
sacs and fibrinous adhesions within the body cavity,
and P. multocida was isolated from the lungs and air
sacs. All five carcasses were collected in California,
one each in January and November of 1978, two in
January of 1985, and one in January of 1988. Pas-
teurellosis, or avian cholera, is an endemic disease
of wintering waterfowl in California, where yearly
losses of ducks and geese numbering in the tens of
thousands are commonplace (Botzler 1991). Pasteu-
rellosis was reported from a red-tailed hawk col-
lected in California in 1982 (Brogden and Rhoades
1983). Reports in raptors are infrequent, although
they are often exposed to the organism when scav-
enging on carcasses of waterfowl that have died of
avian cholera.

Mycobacteriosis (tuberculosis) was diagnosed in
four hawks, including three in which tuberculosis
was the primary finding. Tuberculosis is caused by
bacteria of the genus Mycobacterium, including sev-
eral species with a predilection for birds. The disease
can be acquired by carnivorous birds that ingest the
bacteria in tissues of infected prey, or may be spread
among ground-feeding birds through fecal contam-
ination of soil or food. The characteristic lesions of
avian tuberculosis are nodules located along the gas-
trointestinal tract or in various organs. The affected
red-tailed hawks were found in Wisconsin in 1976
and 1978, Illinois in 1977, and California in 1985.
Typical nodular lesions were found in liver and lung,
liver, spleen, and sternum; liver and spleen; and
proventriculus, respectively. In all cases, character-
istic acid-fast bacteria were seen on histopathology
and in two cases tissues were sent to the National
Veterinary Services Laboratories, Ames, Iowa, where
Mycobacterium avium was isolated.

Avian pox, characterized by proliferative lesions
on unfeathered skin of the feet and face, was noted
in three birds. These hawks were found in Wisconsin
in 1985, in Utah in 1987, and in Nebraska in 1988.

Franson et al.

VoL. 30, No. 1

Intracytoplasmic inclusions consistent with pox were
seen in tissues of all three hawks, and pox virus was
isolated from lesions of one bird. Viral enteritis was
diagnosed in one bird and protozoal enteritis in an-
other by histologic examination of tissues, but at-
tempts to further characterize these agents were un-
successful. One hawk had splenitis and severe pneu-
monia, with consolidation of part of one lung and
thickening of the air sacs. Klebsiella pneumoniae was
isolated from the spleen and Pseudomonas sp. was
isolated from the spleen, liver, and air sac.

Other Diagnoses. Electrocution was diagnosed
in six carcasses with burn marks on feathers or skin,
four of which were found in close proximity to utility
lines. One red-tailed hawk had injuries to a foot and
wing as the result of having been caught in a leg-
hold trap. Miscellaneous conditions (V = 10) of
uncertain etiology included visceral gout (2), peri-
tonitis (2), verminous enteritis (2), pneumonia (1),
sinus abscess (1), and air sacculitis (1). These di-
agnoses were based on gross observations only. His-
topathology revealed hepatitis of unknown origin in
one bird.

Summary. Because of biases inherent in the non-
random collection and submission of carcasses, the
true relative significance of these causes of mortality
on red-tailed hawk populations cannot be deter-
mined. However, these cumulative findings provide
baseline data on a variety of factors that cause mor-
tality in red-tailed hawks, against which future di-
agnostic surveillance can be compared. Of the 131
carcasses for which diagnoses were determined, 39
(30%) died as a result of anthropogenic causes (tox-
icoses, gunshot, electrocution, and trapping). In ad-
dition, a portion of the 29 trauma cases were ap-
parently the result of collisions with man-made
structures. Steps can be taken to reduce these mor-
talities by providing education to increase public
awareness of the impact of human activities on red-
tailed hawks. Future research might be designed to
identify significant temporal and geographic pat-
terns of anthropogenic causes of mortality in red-
tailed hawks, monitor pesticide poisonings, identify
causes of undetermined mortality and emaciation,
and to evaluate population effects of all mortality
factors.

Acknowledgments

We thank the many field biologists who submitted these
carcasses, members of the Resource Health Team at the
National Wildlife Health Center who consulted with field
personnel, and those who conducted necropsies, including

G. Brand, P. Gullett, S. Kerr, J. Langenberg, L. Locke,

H. McAllister, C. Meteyer, T. Roffe, S. Schmeling, L.
Sileo, R. Stroud, and P. Whiteley. Laboratory support
was provided by B. Campbell, R. Cole, and B. Tuggle for
parasitology, R. Duncan for microbiology, and D. Doch-
erty for virology. Chemists at the Patuxent Wildlife Re-
search Center conducted pesticide and selenium analyses;
staff at the Wisconsin Central Animal Health Laboratory
provided additional toxicology support; G. Colgrove, E.
Himes, and C. Thoen of the National Veterinary Services
Laboratories identified mycobacteria; and M. Samuel and
D. Xiang consulted on statistical treatment of data. L.
Blus, L. Locke, G. Preston, and S. Wiemeyer provided
helpful comments on the manuscript.

Literature Cited

Belisle, a. a. and D.M. Swineford. 1988. Simple,
specific analysis of organophosphorus and carbamate
pesticides in sediments using column extraction and
gas chromatography. Environ. Toxicol. Chem.

752.

Blus, L.J., C.J. Henny and R.A. Grove. 1989. Rise
and fall of endrin usage in Washington state fruit or-
chards: effects on wildlife. Environ. Pollut. 60:331-349.
Botzler, R.G. 1991. Epizootiology of avian cholera in
wildfowl. J. Wildl. Dis. 27:367-395.

Boyer, K.W. 1984. Metals and other elements at trace
levels in foods. Pages 444-476 in S. Williams [Ed.],
Official methods of analysis of the Association of Of-
ficial Analytical Chemists, 14th edition. Assoc. Official
Analytical Chemists, Inc., Arlington, VA U.S.A.
Brogden, K.A. and K.R. Rhoades. 1983. Prevalence
of serologic types of Pasteurella multocida from 57 spe-
cies of birds and mammals in the United States. J.
Wildl. Dis. 19:315-320.

Chubb, K. 1987. Avian pox in a red-tailed hawk. Ont.
Bird Banding 19:35.

Clark, F.D. 1986. Mycobacteriosis in a red-tailed hawk
{Buteo jamaicensis). Southwest. Vet. 37:200-201.
Craighead, J.J. and F.C. Craighead, Jr. 1956.
Hawks, owls and wildlife. Stackpole Co., Harrisburg,
PA U S A.

Cromartie, E., W.L. Reighel, L.N. Locke, A. A. Be-
lisle, T.E. Kaiser, T.G. Lamont, B.M. Mulhern,
R.M. Prouty and D.M. Swineford. 1975. Resi-
dues of organochlorine pesticides and polychlorinated
biphenyls and autopsy datafor bald eagles, 1971-1972.
Pestic. Monit. J. 9:11-14.

Dieter, M.P. and J.L. Ludke. 1975. Studies on com-
bined effects of organophosphates and heavy metals in
birds. I. Plasma and brain cholinesterase in coturnix
quail fed methyl mercury and orally dosed with para-
thion. Bull. Environ. Contam. Toxicol. 13:257-262.
Docherty, D.E. and P.G. Slota. 1988. Use of mus-
covy duck embryo fibroblasts for the isolation of viruses
from wild birds. J. Tiss. Cult. Meth. 11:165-170.
Dunning, J.B., Jr. 1984. Body weights of 686 species

March 1996 Postmortems of Red-tailed Hawks 13

of North American birds. West. Bird Banding Assoc.
Monogr. No. 1.

Ellman, G.L., K.D. Courtney, V. Andres, Jr. and
R.M. Featherstone. 1961. A new and rapid col-
orimetric determination of acetylcholinesterase activity.
Biochem. Pharmacol. 7:88-95.

Feldstein, M. 1960. Strychnine. Pages 498-499 in
G.P. Stewart and A. Stolman [Eds.], Toxicology —
mechanisms and analytical methods. Vol. I. Academic
Press, New York, NY U.S.A.

Fitzner, R.E., R.A. Miller, C.A. Pierce and S.E.
Rowe. 1985. Avian pox in a red-tailed hawk {Buteo
jamaicensis) . J. Wildl. Dis. 21:298-301.

Fleming, W.J. AND S.P. Bradbury. 1981. Recovery of
cholinesterase aetivity in mallard ducklings adminis-
tered organophosphorus pesticides. /. Toxicol. Environ.
Health 8:885-897.

FranSON, J.C. 1986. Immunosuppressive effects of lead.
Pages 106-109 in J.S. Feierabend and A.B. Russell
[Eds.], Lead poisoning in wild waterfowl — a work-
shop. Natl. Wildl. Fed., Washington, DC U.S.A.

. 1996. Interpretation of tissue lead residues in

birds other than waterfowl. In W.N. Beyer, G.H. Heinz
and A.W. Redmon [Eds.], Environmental contami-
nants in wildlife: interpreting tissue concentrations.
Lewis Publishers, Boca Raton, FL U.S.A. In Press.

, L. Sileo and N.J. Thomas. 1995. Causes of

eagle deaths. Page 68 in E.T. LaRoe, G.S. Farris,
C.E. Puckett, P.D. Doran and M.J, Mac [Eds.], Our
living resources: a report to the nation on the distri-
bution, abundance, and health of U.S. plants, animals,
and ecosystems. Natl. Biol. Serv., Washington, DC
U.S.A.

Greig-Smith, P.W. 1991. Use of cholinesterase mea-
surements in surveillance of wildlife poisoning in farm-
land. Pages 127-150 in P. Mineau [Ed.], Cholines-
terase-inhibiting insecticides — their impact on wildlife
and the environment. Vol. 2, Elsevier, Amsterdam, The
Netherlands.

Gremillion-Smith, C. and a. Woolf. 1993. Screen-
ing for anticholinesterase pesticide poisoning in Illinois
raptors. Trans. III. State Acad. Sci. 86:63-69.

Halliwell, W.H. 1972. Avian pox in an immature
red-tailed hawk. /. Wildl. Dis. 8:104-105.

Heinz, G.H., D.J. Hoffman and L.G. Gold. 1988.
Toxicity of organic and inorganic selenium to mallard
ducklings. Arch. Environ. Contam. Toxicol. 17:561-568.

Henny, C.J., L.J. Blus, E.J. Kolbe and R.E. Fitzner.
1985. Organophosphate insecticide (famphur) topi-
cally applied to cattle kills magpies and hawks. J. Wildl.
Manage. 49:648-658.

, E.J. Kolbe, E.F. Hill and L.J. Blus. 1987.

Case histories of bald eagles and other raptors killed
by organophosphorus insecticides topically applied to
livestock. J. Wildl. Dis. 23:292-295.

Hill, E.F. 1988. Brain cholinesterase activity of ap-
parently normal wild birds. J. Wildl. Dis. 24:51-61.

AND W.J. Fleming. 1982. Anticholinesterase

poisoning of birds: field monitoring and diagnosis of
acute poisoning. Environ. Toxicol. Chem. 1:27-38.

Hooper, M.J., P.J. Detrich, C.P. Weisskopf and B.W.
Wilson. 1989. Organophosphorus insecticide ex-
posure in hawks inhabiting orchards during winter
dormant-spraying. Bull. Environ. Contam. Toxicol. 42.
651-659.

Hunt, K.A., D.M. Bird, P. Mineau and L. Shutt
1 992. Selective predation of organophosphate-exposed
prey by American kestrels. Anim. Behav. 43:971-976.

Hutton, M. 1981. Accumulation of heavy metals and
selenium in three seabird species from the United King-
dom. Environ. Pollut. 26A: 129-1 45.

JOHNSGARD, P.A. 1990. Hawks, eagles, and falcons of
North America. Smithsonian Inst. Press, Washington,
DC U.S.A.

Krynitsky, A.J. 1987. Preparation of biological tissue
for determination of arsenic and selenium by graphite
furnace atomic absorption spectrometry. Anal. Chem
59:1884-1886.

Ludke, J.L., E.F. Hill and M.P. Dieter. 1975. Cho-
linesterase (ChE) response and related mortality aimong
birds fed ChE inhibitors. Arch. Environ. Contam. Tox-
icol. 3:1-21.

Lumeij, J.T., I. Westerhof, T. Smit and T.J. Spier-
enburg. 1993. Diagnosis and treatment of poisoning
in raptors from the Netherlands: clinical case reports
and review of 2,750 postmortem cases, 1975-1988.
Pages 233-238 in P.T. Redig, J.E. Cooper, J.D. Rem-
ple, D.B. Hunter and T. Hahn [Eds.], Raptor bio-
medicine. Univ. Minnesota Press, Minneapolis, MN
U.S.A.

Mollhoff, W.J. 1983. Avian tuberculosis in a red-
tailed hawk. Nebr. Bird Rev. 51:92-93.

Ohlendorf, H.M., R.L. Hothem, C.M. Bunck and
K.C. Marois. 1990. Bioaccumulation of selenium in
birds at Kesterson Reservoir, California. Arch. Environ
Contam. Toxicol. 19:495-507.

Okoniewski, J.C. and E. Novesky. 1993. Bird poison-
ings with cyclodienes in suburbia: links to historic use
on turf. /. Wildl. Manage. 57:630-639.

O’Meara, D.C. AND J.F. Witter. 1971. Aspergillosis.
Pages 153-162 in J.W. Davis, R.C. Anderson, L. Kar-
stad and D.O. Trainer [Eds.], Infectious and parasitic
diseases of wild birds. Iowa State Univ. Press, Ames,
lA U.S.A.

Pace, L.W., M.M. Chengappa, S. Greer and C. Al-
DERSON. 1987. Isolation of Erysipelothrix rhusiopa-
thiae from a red-tailed hawk {Buteo jamaicensis) with
a concurrent pox virus infection. J. Wildl. Dis. 23:671-
673.

Prijono, W.B. and F.A. Leighton. 1991. Parallel
measurement of brain acetylcholinesterase and the
muscarinic cholinergic receptor in the diagnosis of acute.

Franson et al.

VoL. 30, No. 1

lethal poisoning by anti-cholinesterase pesticides. J.
Wildl. Dis. 27:110-115.

Rocke, T.E. and M.D. Samuel. 1991. Effects of lead
shot ingestion on selected cells of the mallard immune
system. J. Wildl. Dis. 27:1-9.

Rosskopf, W.J., Jr., D. Van De Water and E.B.
Howard. 1987. Response to autogenous vaccination
and recovery by a red-tailed hawk {Buteo jamaicensis)
from avian pox virus infection. Compan. Anim. Pract.
1:39-42.

Santiago, G., P.A. Mills and C.E. Kirkpatrick. 1985.
Oral capillariasis in a red-tailed hawk: treatment with
fenbendazole. /. .(4mcr. Vet. Med. Assoc. 187:1205-1206.
Schuler, C.A., R.G. Anthony and H.M. Ohlendorf.
1990. Selenium in wetlands and waterfowl foods at
Kesterson Reservoir, California, 1984. Arch. Environ.
Contam. Toxicol. 19:845-853.

Senne, D.A. 1989. Virus propagation in embryonating
eggs. Pages 176-181 in H.G. Purchase, L.H. Arp,
C.H. Domermuth and J.E. Pearson [Eds.], A labo-
ratory manual for the isolation and identification of

avian pathogens. Kendall/Hunt Publ. Co., Dubuque,
lA U.S.A.

Smith, M.R., N.J. Thomas and C. Hulse. 1995. Ap-
plication of brain cholinesterase reactivation to differ-
entiate between organophosphorus and carbamate pes-
ticide exposure in wild birds. /. Wildl. Dis. 31:263-
267.

Stone, W.B., S.R. Overmann and J.C. Okoniewski.
1984. Intentional poisoning of birds with parathion.
Condor 86:333-336.

Sykes, G.P. 1982. Tuberculosis in a red-tailed hawk
{Buteo jamaicensis). J. Wildl. Dis. 18:495-499.

White, D.A., K.A. King and R.M. Prouty. 1980. Sig-
nificance of organochlorine and heavy metal residues
in wintering shorebirds at Corpus Christi, Texas, 1976-
77. Pestic. Monit. J. 14:58-63.

Zar, J.H. 1984. Biostatistical analysis. Prentice Hall,
Englewood Cliffs, NJ U.S.A.

Received 31 May 1995; accepted 21 September 1995

J Raptor Res. 30(l):15-20
© 1996 The Raptor Research Foundation, Inc.

NESTING AND FOOD HABITS OF THE FLAMMULATED
OWL {OTUS FLAMMEOLUS) IN SOUTHCENTRAL IDAHO

Leon R. Powers, Allen Dale, Peter A. Gaede, Chris Rodes,

Lance Nelson, John J. Dean and Jared D. May

Department of Biology, Northwest Nazarene College, Nampa, ID 83686 U.S.A.

Abstract. — Flammulated owls (Otus flammeolus) arrived at our 25-km^ study area in Idaho from mid-
to late May 1991-94. Twenty-four nesting pairs utilized 22 nesting cavities. Twenty (83%) of the nests
were in dead trees and four (17%) in live trees. Thirteen (54%) nests were in broken-top Douglas-fir
{Pseudotsuga menziesii) snags, and 1 1 (46%) were in trembling aspen {Populus tremuloides). Mean diameter
at breast height of 13 nest trees was 49.9 cm (SD = 18.9), while mean cavity height was 5.1 m (SD =
0.6). Mean entrance diameter for 11 nests was 6.8 cm (SD — 1.3). Mean hatching date at 11 of the 24
nests was 26 June (range, 12 June through 11 July) and mean fledging date was 18 July (range, 7 July
through 2 August). Mean brood size for nine nests was 2.3 (range, 2-3) young per nest. Nightly food
deliveries at nest sites peaked within the 2-hr period after dark and before daylight. Mean number of
nest visits by adults during the nesting stage was 93. Although lepidopterans comprised 79% and or-
thopterans 0.3% of the available prey within the study area in 1992, 65 food deliveries at one nest revealed
43.1% orthopteran and 9.2% lepidopteran prey. At other nest sites, lepidopterans were the prominent
prey. Four banded owls returned to the same territory for two, three, and four consecutive nesting seasons.

Key Words: flammulated owl\ food habits', Idaho', nesting', Otus flammeolus.

Nidificacion y habitos alimentarios de Otus flammeolus en el centro-sur de Idaho

Resumen. — Otus flammeolus arribo a nuestra area de estudio de 25 km^ en la segunda quincena de mayo
de 1991 a 1994. Veinticuatro parejas nidificantes utilizaron 22 cavidades. Veinte (83%) de los nidos se
ubicaron en arboles muertos y cuatro (17%) en arboles vivos. Trece nidos (54%) se encontraron en ramas
alta quebradas de Pseudotsuga menziesii y 11 (46%) nidos estaban en Populus tremuloides. El diametro
medio a la altura del pecho de 13 arboles con nidos fue 49.9 cm (DS = 18.9). Mientras la cavidad se
ubico a una altura media de 5.1 m (DS = 0.6). El diametro medio para la entrada en 11 nidos fue de
6.8 cm (DS = 1.3). La fecha media de eclosion en 11 de los 24 nidos, ocurrio el 26 de junio (range 12
de junio hasta el 11 de julio). La fecha media del estado volanton fue el 18 de julio (range 7 de julio al
2 de augosto). El tamaho medio de nidada para nueve nidos fue de 2.3 (range 2-3) juveniles por nido.
La alimentacion nocturna en el nido ocurrio en el periodo de dos horas despues de hacerse oscuro y dos
horas antes de la luz diurna. El numero promedio de visitas al nido por adultos, durante el estado de
polio, fue de 93. Aunque los lepidopteros constituian el 79% y los ortopteros el 0.3% de las presas
disponibles en el sitio de estudio en 1992, 65 entregas de alimento en un nido revelaron que las pesas
estaban constituidas por un 43.1% de ortopteros y un 9.2% de lepidopteros. En otros nidos, los lepidopteros
fueron las presas dominantes. Cuatro biihos marcados retornaron al mismo territorio, por dos, tres y
cuatro estaciones de nidificacion consectivas.

[Traduccion de Ivan Lazo]

Until recently the flammulated owl {Otus flam-
meolus) was one of the least-known species of owl
occurring in the mountain forests of western North
America (Reynolds et al. 1989). Ranging from Brit-
ish Columbia to Central America, this small, cavity-
nesting, predominantly insectivorous owl was for-
merly considered rare throughout much of its range
(Bent 1938). Recent studies, however, have found it
to be present in Montana (Holt et al. 1987) and
fairly common in portions of California (Winter 1974,
Marcot and Hill 1980), Colorado (Linkhart and

Reynolds 1987), New Mexico (McCallum and
Gehlbach 1988), Oregon (Bull and Anderson 1978,
Goggans 1986, Bull et al. 1990) and British Colum-
bia (Cannings et al. 1978, Howie and Ritcey 1987).
The flammulated owl is presumed to be migratory
at least within the Canadian and United States por-
tions of its range (Reynolds et al. 1989) with sup-
porting evidence for such being documented in New
Mexico and Arizona (Baida et al. 1975).

Flammulated owls occur in Idaho (Larrison et al.
1967, Burleigh 1971) and although their distribution

Powers et al.

VoL. 30, No. 1

and nesting status have been documented (Hayward
1986, Atkinson and Atkinson 1990, Moore and
Frederick 1991), their breeding biology has received
little study within the state. Currently the owl is
listed as a species of special concern by the Idaho
Department of Fish and Game and as a sensitive
species (Moseley and Groves 1994). The status of
this owl is in further jeopardy because it is a Neo-
tropical migrant (Saab and Groves 1992). Objectives
of our study were to document the occurrence, nest-
ing activities and food habits of flammulated owls
in the west portion of the Sublett Mountains during
four nesting seasons, 1991-94.

Study Area and Methods

The Sublett Mountains are approximately 68 km south-
east of Burley, Cassia County, Idaho on the east edge of
the Raft River Valley. Scattered Utah juniper (Juniperus
osteosperma) communities skirt the lower regions and iso-
lated pockets of trembling aspen (Populus tremuloides) and
Douglas-fir (Pseudotsuga menziesii) are found at upper
elevations, especially along north-facing slopes and draws.
Our study area encompassed six dry canyons running
north into the South Fork of Sublett Creek drainage. To-
pography is characterized by narrow canyon bottoms and
moderate side slopes with elevation ranging from 1540-
2200 m. Annual precipitation, primarily snow, varies from
25-75 cm and temperatures range from — 37-38°C (J.
Chard pers. comm.). Forest vegetation is predominantly
aspen and Douglas-fir. Vegetation types in the study area
are primarily sagebrush-grass, mountain shrub, riparian
with scattered forbs, and grassland types. With the ex-
ception of scattered springs or seeps, there is no running
water in any of the canyons studied.

Approximately 8 km^ in Beaverdam and Twin Canyons
were surveyed for owls in 1991. We expanded our surveys
to approximately 25 km^ in 1992 including an unnamed
canyon (“Fenceline”), Kossman, and Eyrie Springs Can-
yons.

In 1991 our study efforts centered in Beaverdam Can-
yon where field studies were conducted between 5 April
and 22 September. During 1992 we continued our studies
in Beaverdam Canyon between 15 May and 26 June, and
on 26 June we expanded our study into “Fenceline,”
Kossman and Eyrie Canyons, visiting all three canyons
between 27 June and 15 November. In 1993 field work
was conducted within the entire study area between 10
May and 28 July. The 1994 study season began on 25
May and continued through 12 August. We visited each
suspected and known nest site at least once each trip to
the study area. Previous incidental observations on nest
sites, nesting phenology and banding efforts in the study
area by one of us (LP) dating back to 1983 are also in-
cluded with these data.

During April (1991 only), May, and June we conducted
nocturnal surveys of the study area using playbacks of
tape-recorded calls between sunset and midnight. Areas
where responses were obtained were flagged for diurnal
revisitation and investigation. All living trees and snags

bearing cavities were scratched (Bull et al. 1990) for de-
termination of occupancy two or three times during June
and July. In addition, we sometimes skylighted cavities
(Reynolds and Linkhart 1984) and made nocturnal ob-
servations with night-vision optics to determine occupancy
and stage of nesting phenology at their cavities. Activity
at nest cavities was monitored by periodic diurnal visits,
to confirm nocturnal visitation by adults, and nestling or
fledgling food-begging vocalizations. All-night observa-
tions recording the time and number of adult nest visits
were on two nights each at two nests.

At least once each trip to the study area, nocturnal prey
was sampled with a standard black-light (ultraviolet) and
1.5 X 1.5 m framed sheet sampling station. Insect sampling
was always done within one of the occupied owl territories.
Insects captured were measured and categorized into size
classifications of small (8-11 mm), medium (12-13 mm)
or large (14-32 mm) body length (Baida et al. 1975). To
determine prey selection, we photographed prey deliveries
and visually documented prey by close observations of
artificially lighted nest cavities.

To determine nest site and mate fidelity and document
individual activities at nest sites, owls were trapped and
banded whenever possible. Adult owls were captured ei-
ther in hand nets or mist nets placed in front of occupied
nest cavities. All owls were banded with U.S. Fish and
Wildlife Service aluminum bands.

Results

Owls were first detected in the study area from
mid- to late-May each year with the earliest date
being 16 May 1993. April and early May playback
tape surveys in the study area produced no vocalizing
or other evidence of their presence. In the latter part
of May and early June territorial calling by males
and pair-bonding behavior, such as food solicitation
callings (mewing) by females and allofeeding by males
(McCallum 1994a), became more evident about pro-
spective cavities. Such behavior was observed at three
territories during the night of 9 June 1993.

Twenty-four nesting attempts by flammulated owls
utilized 22 different nest cavities during our study
(two of the cavities were occupied twice in consec-
utive years). Including previous observations of an
active nest in 1983 and two others in 1988, 14 nests
were found in Beaverdam Canyon, one in west Twin
Canyon, four in Kossman Canyon, two in Eyrie
Canyon and three occurred in “Fenceline” canyon
between Twin and Kossman Canyons. The number
of known nesting pairs was three in 1991, four in
1992, eight in 1993 and six in 1994.

We were able to determine brood size at only nine
of our 24 nests. Single fledglings were observed at
two additional nests. Three of the nine nests pro-
duced three nestlings each and the rest contained
two young each {x = 2.3).

March 1996

Flammulated Owl Nesting Biology

Night of 25 July 1991

Night of 23 July 1992

Night of 29 July 1991 plight of 28 July 1992

Figure 1. Nest visits by flammulated owls at Side Can- Figure 2. Nest visits by flammulated owls at Eyrie Can-
yon during the nights of 25 July (a) and 29 July (b), 1991. yon during the nights of 23 July (a) and 28 July (b), 1992

Twenty (837o) of the owl nests were in dead trees
and four (17%) in live trees. Of these, 13 (54%) were
in dead broken-top Douglas-fir snags and 1 1 (46%)
in trembling aspens — seven (29%) in dead trees and
four (17%) in live aspens. Mean dimensions for 13
nest sites were 49.9 cm (SD = 18.9) for diameter at
breast height, 5.1 m (SD = 0.6) for cavity height;
entrance diameter for 11 of the nests was 6.8 cm
(SD = 1.3). Primary excavators of cavities within
our study area were the northern flicker (Colaptes
auratus), hairy woodpecker {Picoides villosus) and the
yellow-bellied sapsucker (Sphyrapicus varius).

We were able to determine hatching or fledging
dates at 1 1 of the 24 nests. Using 22 d for both the
incubation and nestling periods (Reynolds and Link-
hart 1987, Johnsgard 1988, McCallum 1994a) we

calculated the mean hatching date for the 11 nests
as 26 June (range, 12 June through 11 July) and
mean fledging date as 1 8 July (range, 7 July through
2 August).

During the nestling stage at two nests, four all-
night surveillances (Figs. 1 and 2) recorded 65, 93,
133, and 81 (x = 93) nocturnal nest visits by adult
owls, primarily the male. These nightly food deliv-
eries at nest sites peaked within the 2-hr periods
after dark and before daylight.

Insect sampling in 1992 (Tables 1 and 2) recorded
more smaller-sized invertebrates (37.6%) compared
to larger potential prey (27.4%) and found lepidop-
terans to comprise 78.8% and orthopterans 0.3% of
the prey sampled within the study area. Photograph-
ic analysis (Table 3) of 65 food deliveries at one nest

Powers et al.

VoL. 30, No. 1

Table 1. Invertebrate sizes recorded at black-light sampling stations within the study area, summer 1992.

Locality

Date

Number by Size Class

Small (8-11 mm)

Medium (12-13 mm)

Large (14-1- mm)

Beaverdam Canyon

25 June

2 July

Kossman Canyon

3 July

Eyrie Canyon

8 July

13 July

14 July

23 July

24 July

Totals

245

228

179

(37.6%)

(35.0%)

(27.4%)

identified 43.1% as orthopterans and 9.2% as lepi-
dopterans. Observations at other nests (Table 3) re-
vealed a predominance of lepidopteran prey.

A female owl was captured in the same territory
in 1992, 1993 and 1994; nesting in the same cavity
the first 2 yr but in a different snag the third year.
Her mate was not banded in 1992 but was known
to occupy that territory in 1993 and 1994. Another
male nested in different snags 60 m apart in 1991
and 1993, but could not be identified during 1992
and 1994 when no occupied nests could be found
within that territory, A third male, nesting in 1988
was recaptured again in 1991 in a mist net 50 m
from the 1988 nest tree. We did not sample the area
between 1988 and 1991.

Discussion

Although spring arrival dates for flammulated owls
in Idaho are not well-documented, the mid- to late-
May arrivals in our study area seem comparable to

Table 2. Invertebrates recorded at black-light sampling
stations in the study area, summer 1992.

Invertebrate

Number

Sampled

Percent

Lepidoptera

514

78.8

Diptera

112

17.2

Coleoptera

2.3

Dermaptera

1.1

Orthoptera

0.3

Arachnida

0.3

Totals

652

100

the few records elsewhere in the state. For example,
singing owls were heard on 10 May in the Salmon
National Forest (Atkinson and Atkinson 1990), on
24 May 1991 in westcentral Idaho (Moore and
Frederick 1991), and a migrating flammulated owl
was photographed roosting in a black-billed magpie
{Pica pica) nest near Boise, Ada County, Idaho on
16 May 1970 (E. Thompson pers. comm.). Owls
may have arrived earlier in May some years since
the number of consecutive days we spent in the study
area was limited and inclement weather occasionally
prevented our early access to the study area.

Reynolds and Linkhart (1992) reported that with
the exception of a single nest in a pinon pine {Pinus
edulis) in California, all reported nests of the flam-
mulated owl occur in forests containing at least some
ponderosa pine {Pinus ponderosa). Recent studies
have found this owl mostly avoiding the ponderosa
pine belt in southern British Columbia (Howie and
Ritcey 1987) and nesting in forests devoid of this
pine in Nevada (S. Garland pers. comm.). Our study
provides another exception in that ponderosa pine
does not occur within our study area. Douglas-fir
and aspen were the only tree species utilized by
nesting owls in our study. Although this owl is known
to occur in trembling aspen (Webb 1982), the high
incidence of its utilization of this tree species for nest
sites in our study area (46%) is apparently much
greater than reported elsewhere. Our findings con-
tribute to the mounting evidence that flammulated
owls may not be so exclusively tied to ponderosa pine
as much of the earlier literature indicates.

Nesting phenology is not well-documented for the
flammulated owl throughout its range. In Colorado

March 1996

Flammulated Owl Nesting Biology

Table 3. Prey delivered to four flammulated owl nests, 1991-93.

Prey Category

199U

1992b

1993^

Totals

Orthoptera

1 (4.3%)

28 (43.1%)

5 (13.97o)

34 (27.4%)

Coleoptera

0(0)

5 (7.7%)

0(0)

5 (4.0%)

Diptera

3 (13.0%)

0(0)

3 (2.4%)

Lepidoptera

9 (39.1%)

6 (9.2%)

29 (80.5%)

44 (35.5%)

Larva

10 (43.5%)

2 (3.1%)

2 (5.6%)

14 (11.3%)

Unidentified

0(0)

24 (36.9%)

0(0)

24 (19.4%)

Totals

124

^ Beaverdam/Side Canyon nest (29 July, dusk-to-dawn observations).

^ Photographic analysis of prey delivered to Eyrie Canyon nest (23 and 28 July, dusk-to-dawn observations).
Beaverdam/Side Canyon nest and Beaverdam Base Camp nest (7, 8, 18 and 27 July, partial-night observations).

the mean date at which the last egg hatched was 29
June (Reynolds and Linkhart 1987) and 30 June
was given as the hatching date at a single flammu-
lated owl nest in southwestern Idaho (Hayward

1986) . Our mean hatching date (26 June) may seem
early considering the northern extent of our study
area and the migratory demands on our owls com-
pared to the more southern Colorado birds. How-
ever, even though more southern in latitude, the 350-
1300 m higher elevation of the Colorado habitat
where snow lingered until early May (Reynolds and
Linkhart 1987), likely places their owls into a sim-
ilar nesting phenology.

Productivity data from our study are limited but
the observed brood size (x = 2.3) of nine nests ap-
pears lower than reported for most other populations
(McCallum 1994a) except in New Mexico (Mc-
Callum et al. 1995), and may support the view that
ponderosa pine is the most productive habitat for
this owl, even if not the only one used (D.A.
McCallum pers. comm.).

In southwest Idaho, Hayward (1986) recorded
54-97 nest visits per night by adults during 9 d of
the nestling period. Numerous nocturnal observa-
tions by Reynolds and Linkhart (1987) at nests in
Colorado all terminated at 0300 H and thus cannot
be directly compared to either Hayward’s (1986) or
our data. However, the food delivery rate at Colo-
rado nests peaked at over 16 trips per hour during
the 8-12 d after hatching (Reynolds and Linkhart

1987) . Our maximum nest visits per night (133) and
peak visits per hour (>30; Figs. 1 and 2) exceed
those reported elsewhere. Like Hayward (1986), we
observed a greater number of food deliveries early
in the night, following the lengthy diurnal fasting
period.

Although small vertebrate prey has been docu-
mented at flammulated owl nests (Linkhart and
Reynolds 1994), as elsewhere (Hayward 1986,
Reynolds and Linkhart 1987) we observed only in-
vertebrate prey, predominantly small lepidopterans,
being delivered to nests. Orthopterans, which com-
prised only a minor part of this owl’s food in other
studies (Hayward 1986, Reynolds and Linkhart
1987, McCallum 1994a), were the predominant prey
(43.1%) during the late nestling stage at one of our
1992 nests (Table 3), despite their concurrent low
incidence at the black-light sampling stations within
the study area (Table 2). During that same time,
we observed a general surge of crepuscular and noc-
turnal activity of the shield-backed katydid {Neduba
carinata) along roadside areas in proximity to the
nest, suggesting that the owls were opportunistically
utilizing this abundant food source. Otherwise, prey
selection at our nests followed the usual predomi-
nance of lepidopterans (Table 3). Goggans (1986)
found that food habits of Oregon owls shifted from
noctuid moths early in the summer to orthopterans
later. Our sampling of potential prey with the black-
light station seemed effective for most nocturnal in-
sects but did not attract many orthopterans (pers.
obs.), hence their scarcity in our samples may merely
reflect a sampling bias.

Acknowledgments

We are very grateful for the financial support provided
this project by a grant from M.J. Murdock Charitable
Trust for the encouragement of undergraduate research.
Research Corporation’s Partners in Science program also
supported one of our team members (A.D.) for 2 yr of the
study. We wish to thank Jon Beals, Gary Burkholder,
and Steve Wilcutts who assisted us at times on fieldwork
We are very grateful to D.W. Holt, D.A. McCallum and

Powers et al.

VoL. 30, No. 1

V. Wright for helpful comments of an earlier draft of this

paper.

Literature Cited

Atkinson, E.C. and M.L. Atkinson. 1990. Distribu-
tion and status of flammulated owls in the Salmon
National Forest. Idaho Dept. Fish Game, Coop. Cost-
Share Proj., Boise, ID U.S.A.

Balda, R.P., B.C. McKnight and C.D. Johnson. 1975.
Flammulated owl migration in the southeastern United
States. Wilson Bull. 87:520-523.

Bent, A.C. 1938. Life histories of N orth American birds
of prey (part 2). U.S. Natl. Mus. Bull. 170. Wash-
ington, DC U.S.A.

Bull, E.L. and R.G. Anderson. 1978. Notes on flam-
mulated owls in northeastern Oregon. Murrelet 59: 26-
28.

, A.L. Wright AND M.G. Henjum. 1990. Nest-
ing habitat of flammulated owls in Oregon. /. Raptor
Res. 24:52-55.

Burleigh, T.D. 1971, Birds of Idaho. Caxton Printers
Ltd. Caldwell, ID U.S.A.

Cannings, R.J., S.R. Cannings, J.M. Cannings and
G.P. SiRK. 1978. Successful breeding of the flam-
mulated owl in British Columbia. Murrelet 59:75.

Goggans, R. 1986. Habitat use by flammulated owls
in northeastern Oregon. M.S. thesis, Oregon State
Univ., Corvallis, OR U.S.A.

Hayward, G.D. 1986. Activity pattern of a pair of
nesting flammulated owls {Otus flammeolus) in Idaho.
Northwest Sci. 60:141-144.

Holt, D.B., J.A. Hoy and P.L, Wright. 1987. Oc-
currence and first nest record of flammulated owls in
Montana. J. Raptor Res. 21:121-124.

Howie, R.R. and R. Ritcey. 1987. Distribution, hab-
itat selection, and densities of flammulated owls in
British Columbia. Pages 249-254 in R.W. Nero, R.J.
Clark, R.J. Knapton and R.H. Hamre [Eds.], Biology
and conservation of northern forest owls. USDA For,
Serv. Gen. Tech. Rep. Rm-142, Ft. Collins, CO U.S.A.

Johnsgard, P.A. 1988. North American owls. Smith-
sonian Inst. Press, Washington, DC U.S.A.

Larrison, E.J., J.L. Tucker and M.T. Jollie. 1967.
Guide to Idaho birds. J. Idaho Acad. Sci. 5:1-120.

Linkhart, B.D. and R.T. Reynolds. 1987. Brood di-
vision and postnesting behavior of flammulated owls.
Wilson Bull. 99:240-243.

AND . 1994. Peromyscus carcass in the

nest of a flammulated owl. J. Raptor Res. 28:43-44.

McCallum, D.A. 1994a. Flammulated owl. In A. Poole

and F. Gill [Eds.], The birds of North America, No.
93, Acad. Nat. Sci., Philadelphia, PA and Am. Or-
nithol. Union, Washington, DC U.S.A.

AND F.R. Gehlbach. 1988. Nest-site prefer-
ences of flammulated owls in western New Mexico.
Condor 90:653-661.

, AND S.W. Webb. 1995. Life history of

flammulated owls in a marginal New Mexico popu-
lation. Wilson Bull. 107:530-537.

Margot, B.G. and R. Hill. 1980. Flammulated owls
in northwestern California. Western Birds 11:141-149.

Moore, T.L. AND G.P. Frederick. 1991. Distribution
and habitat of flammulated owls in west central Idaho.
Idaho Dept. Fish Game, Challenge Cost-Share Proj.,
Boise, ID U.S.A.

Moseley, R. and C. Groves. 1994. Rare, threatened
and endangered plants and animals of Idaho. Cons.
Data Center, Idaho Dept. Fish Game, Boise, ID U.S.A.

Reynolds, R.T. and B.D. Linkhart. 1984. Methods
and materials for capturing and monitoring flammu-
lated owls. Great Basin Nat. 44:49-51.

AND . 1987. The nesting biology of flam-
mulated owls in Colorado. Pages 239-248 in R.W
Nero, R.J. Clark, R.J. Knapton and R.H. Hamre
[Eds.], Biology and conservation of northern forest owls.
USDA For. Serv. Gen. Tech. Rep. Rm-142, Ft. Col-
lins, CO U.S.A.

AND . 1992. Flammulated owls in pon-

derosa pine: evidence of preference for old growth.
Pages 166-169 in M.R. Kaufmann, W.H. Moir and
R.L. Basett [Tech. Coords.], Old-growth forests in
the Southwest and Rocky Mountain regions. USDA
For. Serv. Gen. Tech. Rep. RM-213, Ft. Collins, CO
U.S.A.

, R.A. Ryder and B.D. Linkhart. 1989. Pages

134-143 in K.S. Steenhof, M.N. Kochert and M.N
LeFrance [Eds.], Small forest owls. Proc. Western
Raptor Manage. Symp. Workshop, Natl. Wildl. Fed
Sci. Tech. Ser. No. 12, Washington, DC U.S.A.

Saab, V. and C. Groves. 1992. Idaho’s migratory land
birds. Idaho Wildl. 12:1-16.

Webb, B. 1982. Distribution and nesting requirements
of montane forest owls in Colorado, Pt. II: flammulated
owl {Otus flammeolus). J. Colo. Field Ornithol. 16:76-
81.

Winter, J. 1974. The distribution of the flammulated
owl in California. Western Birds 5:25-44.

Received 28 March 1995; accepted 17 September 1995

J. Raptor Res. 30(l):21-27
© 1996 The Raptor Research Foundation, Inc.

BREEDING, GROWTH, DEVELOPMENT, AND
MANAGEMENT OF THE MADAGASCAR FISH-EAGLE

{HALIAEETUS VOCIFEROIDES)

Richard T. Watson, Simon Thomsett,' Donna O’Daniel and

Richard Lewis

The Peregrine Fund, 5666 West Flying Hawk Lane, Boise, ID 83709 U.S.A.

Abstract. — Increasing population size and distribution in suitable unoccupied habitat is one of several
management options that would help prevent the extinction of the Madagascar fish-eagle {Haliaeetus
vociferoides) , one of the rarest raptors in the world. Breeding studies from 1991 through 1994 show this
species exhibits siblicide or Cainism. In 1993 we tested sibling rescue as a low-cost in situ method for
increasing annual production of Madagascar fish-eagles. Of three nests tested, two fledged two young
using an abbreviated captive rearing period in which removed siblings were reintroduced to artificially
enlarged nests as soon as they could defend themselves from siblings and compete for food. Sibling rescue
increased production from four to six young from a sample of 10 nests. Measurements of weight gain,
feather development and description of the behavioral development of chicks in captivity and in the nest,
provide new information and a better understanding of siblicide in this little studied species.

Key Words; Cainism; conservation; development; growth; Madagascar; management; siblicide.

Reproduccion, crecimiento, desarrollo y manejo de Haliaeetus vociferoides

Resumen.' — Incremento del tamano poblacional y distribucion en habitat adecuados pero no ocupados,
es una de las varias opciones que podrian prevenir la extincion de Haliaeetus vociferoides, uno de los
rapaces mas raros del mundo. Desde 1991 a 1994, estudios de reproduccion mostraron que esta especie
exhibe fratricidio o Cainismo. En 1993, probamos el rescate de hermanos como metodo in situ, de bajo
costo, para incrementar la produccion anual de esta aguila. De los tres nidos probados, dos volantones y
dos juveniles fueron sometidos a un corto periodo de crianza y reintroducidos artificialmente en grandes
nidos. Esto ocurrio tan pronto como fueron capaces de defenderse de sus hermanos y competir por el
alimento. El rescate de hermanos aumentoo la produccion de cuatro a seis juveniles en una muestra de
10 nidos. Medidas de ganancia de peso, desarrollo de plumaje y descripcion conductual de polluelos en
cautividad y nido, permiten proveer nueva informacion y una mejor comprension del fenomeno de
fratricidio.

[Traduccion de Ivan Lazo]

The Madagascar fish-eagle {Haliaeetus vocifer-
oides) is one of the rarest birds of prey in the world
with a population size estimated at 50-70 breeding
pairs (Langrand and Meyburg 1989, Watson and
Rabarisoa 1995). Habitat degradation is one cause
of the species’ rarity but persecution, and other fac-
tors have reduced its density even where suitable
habitat remains (Watson et al. 1993). Increasing
population size and distribution in suitable unoc-
cupied habitat is one of several management options
that would help prevent extinction of the species.

Meyburg (1983) suggested sibling rescue as a
technique for increasing annual production in birds
of prey that exhibit sibling aggression in the absence

' Present address: P.O. Box 42818, Nairobi, Kenya.

of food shortage, known as siblicide or Cainism. He
used the Madagascar fish-eagle as an example of an
endangered species that may benefit from this form
of management. Langrand and Meyburg (1989) sur-
mised that siblicide was the basis for their obser-
vation that only one young was produced in each of
three nests despite two eggs being laid in each. Be-
tween 1991 and 1994 we observed breeding success
in Madagascar fish-eagles to determine the fre-
quency of siblicide in this species.

In 1993 we tested sibling rescue, a technique pi-
oneered by Meyburg (1978, 1983) in lesser spotted
eagles {Aquila pomarina) and Spanish imperial ea-
gles (T. heliaca) and demonstrated in black eagles
{A. verreauxii; Gargett 1990, S. Thomsett pers. obs.;
N = 3), augur buzzards Buteo rufofuscus augur (S.
Thomsett pers. obs.; N = 1) and African hawk-eagles

Watson et al.

VoL. 30, No. 1

Table 1. Breeding of Madagascar fish-eagles on Lakes Befotaka, Soamalipo and Ankerika in 1993.

Pair Name

Clutch

Size

Number

Hatched

Sibling

Rescue

Attempted

Number

Fledged

Cause of Failure

Ankerika- 1

Possibly infertile egg

Ankerika-2

Yes

Ankerika- 3

Infertile egg

Ankerika-4

Did not nest

Ankerika- 5

Infertile eggs

Befotaka- 1

Adults disappeared soon after breeding began

Befotaka-2

Fertile eggs deserted

Befotaka-3

Yes

Soamalipo- 1

Eggs covered by nest material

Soamalipo-2

Yes

Chick fell and died

Total 15

® Chick A fell from nest and died, chick B injured when nest fell from tree but later rehabilitated. Without human intervention, this figure
may have been zero.

Hieraaetus spilogaster (S. Thomsett pers. obs.; N =
2), as a low-cost in situ method for increasing annual
production in the Madagascar fish-eagle (O’Daniel
1995). In other species with siblicide, sibling ag-
gression may diminish after 4-6 wk of age (e.g.,
African fish-eagles [Haliaeetus vociferoides]; Brown
1980) or it may continue throughout the nestling
period, as demonstrated in experiments with black
eagles (Gargett 1990). The procedure for sibling
rescue has typically been to separate siblings for six
or more weeks, leaving one in the nest and rearing
the other by hand, followed by exchanging siblings
weekly and ending with reintroduction of removed
siblings to the nest for rearing to independence by
their parents (Gargett 1990). By 6 wk, either levels
of aggression have declined to allow coexistence, or
chicks are capable of avoiding siblings in nests that
are large enough to accommodate them (Gargett
1990).

In this experiment, we tested whether removal of
one chick from its sibling for 3-4 wk until both
appeared large enough to avoid siblings and compete
for food in the nest would result in both young sur-
viving to fledging after reintroduction of the removed
siblings. This technique of abbreviated captive rear-
ing (i.e., not for the full nestling period) minimized
the time of human involvement, while also reducing
the costs and equipment needed.

Methods

Breeding was observed in 65 Madagascar fish-eagle
nests between 1991 and 1994 (Watson et al. 1993). Nest

contents were observed two to three times during each
breeding season using the least intrusive method possible
(in order of preference; binoculars from a distance, mirror
pole from below nest, and climbing to nest) to determine
clutch size, hatching rate and fledging rate. Logistics pre-
vented obtaining complete data sets for all known pairs.

Sibling reseue was tested at three nest sites on Lakes
Befotaka, Soamalipo, and Ankerika, respectively, in west-
ern Madagascar during the 1993 breeding season (May
through November). Breeding pairs were observed at 2-
7 d intervals to determine the number of eggs laid and
hatching dates using least intrusive methods (as above)
required to obtain the information. Of 10 pairs observed,
three hatched two eggs each (Table 1).

The first-hatched nestling from each nest was removed
within 2-8 d after hatching (after the second egg had
hatched) and raised in a brooder for 10-22 d before being
exchanged with its sibling for a similar period. A total of
six chicks were thus held in captivity, and all were color-
banded before being returned to the nest. Swapping brood
mates allowed both to experience being fed by parents
without interference from the sibling, which we assumed
might help with habituation to parents and imprinting on
conspecifics.

Brooders consisted of plastic bowls about 40 cm in di-
ameter, lined with plastic doormat material that was cleaned
daily. Brooders were heated by kerosene lamps at night
and cotton towels were added for chicks less than about 3
wk old to help them keep warm. Bowls were surrounded
by a vertically placed rigid clear plastic sheet which al-
lowed adjacent chicks to see but not contact each other. It
also caught feces. A large aluminum bowl was inverted
and suspended above the brooder to help reduce drafts
and maintain warmth while allowing free circulation of
air.

Chicks were fed locally captured fresh fish {Tilapia spp.)
with a calcium-rich vitamin supplement. While in captiv-
ity, chick weight was measured before and after every

March 1996

Madagascar Fish- Eagle Management

feeding using 1-kg or 3-kg Pesola scales. Behavior was
described ad libitum, usually whenever new behaviors were
noticed. Development of feathers (proportion of down re-
maining on each of the wing, back, breast and head) was
visually estimated, and growth of tarsus, longest primary,
and center tail feather was measured to the nearest mil-
limeter.

The first reintroduction of a chick with its sibling was
attempted when captive chicks showed the ability to defend
themselves against conspecific attack. Aggression and de-
fense was tested by placing two non-sibling chicks together
in the same brooder or by using styrofoam models of chicks
to elicit a response. All chicks were observed for at least
45 min after reintroduction to siblings to ensure that no
fatal aggression occurred.

The chicks and adults at Befotaka-3 nest were observed
for 59 h on 12 d between 17 September (chicks aged 55
and 59 d, respectively) and 1 October 1993, using a 15-
25 X zoom telescope. The first 2 d of observation were
from a blind built in a tree 100 m north of the nest. The
remaining observations were done from 400 m east across
the lake on the opposite shore. The second chick had been
reintroduced to the nest on 24 August and both were within
about 1 mo of fledging when observations began.

Results

Breeding. Of 65 observed breeding attempts be-
tween 1991 and 1994, 17 pairs laid two-egg clutches,
two pairs laid one-egg clutches, and clutch size of
the remainder was undetermined. No nests success-
fully fledged two young, 33 fledged one young, and
the remainder fledged no young. Of six nests known
to hatch two chicks, all raised only one young, the
second to hatch dying within 1 0 d after hatching. In
these cases one egg hatched 2-4 d before the second,
and the first-hatched chick almost doubled in weight
before the second egg hatched. Sibling mortality was
apparently related to observed aggression (O’Daniel
1995, Thomsett pers. obs.) by the older sibling caus-
ing death by battering, starvation or displacement
of the younger chick from the nest.

Growth and Feather Development. Chicks were
completely covered by white down until 16 d old,
when brown contour and flight feathers first ap-
peared on the head and wings. Down was lost from
the head first; heads were fully feathered by about
45 d of age. The fleshy part of the wings lost all
their down by about 55 d, the breast by 74 d and
the back by about 76 d. Flight and tail feathers first
emerged at 17 and 21 d, respectively, the longest
primary (third from outermost) growing to a maxi-
mum length of 400 mm by 90 d (linear regression,
a = -91.26, b = 5.47, = 0.99, P < 0.001) and

center tail feather to 260 mm by 98 d (linear re-
gression, a = —71.71, b — 3.39, = 0.96, P <

0.001) respectively. Tarsus length increased from 20
mm at 3 d to about 60 mm at 20 d and 100 mm at
45 d (linear regression, a = 19.25, b = 2.13, =

0.96, P < 0.001). Claws turned from pale olive at
hatching to predominantly black by 16-18 d of age
and the intact egg tooth dropped off the bill by 23 d.

Weights taken before first feeding of the day fol-
lowed a typical sigmoid growth curve, from 80 g at
3 d after hatching up to about 2500 g at 54 d. Data
were pooled for all chicks because no single chick
was measured from hatching through fledging.
Gompertz, logistic, and von Bertalanffy growth
models were tested using nonlinear least squares
method (Wilkinson 1990). The Gompertz model
provided the best fit (r^ = 0.98, asymptotic mass, A
= 2584 g, mass at zero days, B = 42.2 g, growth
constant, k = 0.057). Females are probably slightly
larger than males, with about 3000 g being the weight
of a fully developed female, as identified from ob-
served copulation of banded adults {N = 2).

Captive fish-eagle chicks, when offered food ad
libitum, fed from three to six times per day until
about 20 d old, when the number of feedings dropped
to twice a day. The amount of food eaten per meal
increased from an average of 20 g at 3 d after hatch-
ing to an average of 300 g at about 54 d.

Behavioral Development. An aggressive reac-
tion was observed from chicks aged anywhere from
2-56 d of age. Levels of aggressive behavior varied
considerably among the six chicks held in captivity.
Some were indifferent while others were aggressive
toward other chicks or models of chicks.

A chick <25 d old, when pecked by a larger chick,
would instantly bow its head and remain that way
for 2-3 min whether attacked again or not. The same
response could be elicited by any pinching of the
chick’s neck, even by humans. However, after about
25 d of age the victim would resist the attack by
either moving away or fighting back.

On hatching, chicks were weak and unable to
move. By 8 d chicks could move around the brooder
with wings and legs working together. They could
also stand on the tarsi, preen, and shake the tail.
First pellets were cast between 1 1 and 15 d, by which
time chicks were vocal and active, walking to receive
food. By 12 d chicks were capable of picking up
small pieces of food from a flat surface. Assuming
that, as in other raptor chicks, a neck out and panting
posture indicated that a chick was too warm, while
a head over back posture indicated that a chick was
comfortable or cool, by 13 d chicks tolerated tern-

Watson et al.

VoL. 30, No. 1

peratures from 21-30°C, appearing most comfort-
able at 25“C in dappled sunlight during the day. By

23 d old they could feed themselves while holding
intact fresh fish in their feet. First wing flapping
was seen at this time, with chicks jumping, falling
over and facing into the wind. Chicks were returned
to their nest and older sibling at 26, 31, and 39 d of
age, respectively, after which behavioral develop-
ment was observed in less detail. Chicks at Befotaka-3
fledged at 81-84 d after hatching.

By age 5 d the chicks produced at least three
distinguishable vocalizations: first, a low volume
“peep, peep, peep” call, second, the same call uttered
louder and more frequently and associated with signs
of discomfort (cold or hunger), and third, a mono-
syllabic three-hoot call of similar pitch to the adult’s
descending tone call (similar also to the African fish-
eagle, Brown 1980). By age 10-13 d they began a
new call “gwa, gwa, gwa” usually in “protest” at
not getting food or when cold. This call persisted
and increased in volume and harshness to become
the begging call typical of most immature eagles.

Sibling Rescue. Reintroduction of siblings to
Soamalipo-2, Befotaka-3 and Ankerika-2 nests was
attempted after chicks could avoid, or defend them-
selves, from sibling attack and appeared capable of
tolerating diurnal temperature variation without pa-
rental or human help. Sibling rescue failed in
Soamalipo-2 but succeeded in the other nests. Of 10
known pairs on all three lakes, including the three
manipulated nests, six young fledged, two of which
would not have succeeded without applying sibling
rescue (Table 1).

Reintroduction at Soamalipo-2 nest. Eggs in
Soamalipo-2 hatched on 7 and 9 July, 1 1 and 41 d
ahead of first-hatched eggs in Befotaka-3 (20 and

24 July) and Ankerika-2 (15 and 17 August). We
removed the older of the two chicks (chick A) at age
8 d, reared it in captivity for 10 d, then exchanged
it for its younger sibling (chick B). When removed,
chick A had a mass of 245 g and chick B 155 g.
Chick B was taken from the nest at age 16 d and
mass of 640 g, and exchanged with chick A (580 g,
18 d). Chick B was returned to the nest with its
sibling on August 4 (1200 g, 26 d). Chick A was
not weighed on this date. No aggression was seen
between chicks during 45 min of observation after
reintroduction. The next day at 1630 H both chicks
had full crops. Chick A had a few scratches on the
face. On 7 August, chick A was found dead under
the nest. Injuries indicated the chick had most prob-

ably died as a result of falling from the nest that
day. The dead chick was more developed but weighed
less (1 100 g dead at 30 d) than chick B (1200 g alive
at 26 d), although the mass difference may have been
from water loss after death. In our opinion, the nest
was too small and poorly built to support two chicks.
The frailty of the nest was demonstrated on 14 Au-
gust when a strong wind blew it out of the tree.
Although we believe the chick did not die from sib-
ling attack directly, the possibility exists that it was
driven from the nest by its sibling.

Nest Enlargement and Reintroduction at Befotaka-3
and Ankerika-2 Nests. We enlarged the nests at
Befotaka-3 and Ankerika-2 before the remaining
reintroductions. Both nests appeared small for the
size of a fish-eagle with diameters of nest material
capable of supporting an eagle of less than 1 m (adult
mass ranges from 2150-3000 g, = 6, and wing
length = 520 mm). On 23 August Befotaka-3 nest
was enlarged by weaving a 1-m diameter nest from
local materials, and positioning it next to the original
nest. The chick in the nest at the time (chick A, 1 800
g, 34 d) was transferred to the new nest by 1200 H.
The adult female flew into the new nest at 1330 H.
Chick B (1300 g, 32 d) was placed in the original
nest on 25 August, and a 0.4 m high fence of sticks
built to separate the chicks while allowing each to
be visible to parents. Chick B had been in captivity
for 22 d. It was offered fish on five occasions by the
adult, but appeared frightened by its parents during
the first day. Both chicks were hand fed the following
day and daily until 27 August when they were both
seen to be fed by the parents. On 29 August two
adults were seen feeding one chick each in their
adjacent nests. Both chicks fledged by 16 October.

A similar procedure was used at Ankerika-2 where
an artificial nest (1x2 m) was placed on top of the
original nest on 1 September when the chicks were
exchanged. Chick A was returned to the nest at age
17 d and chick B, aged 16 d, was taken into captivity.
Chick A was left in the nest at 1200 H and was
being attended by the adult female by 1400 H, Chick
B (1400 g, 39 d) was reintroduced to the nest on 24
September, and both fledged after 28 October (exact
date unknown as they were next seen in January
1994).

Behavior of Chicks and Adults in the Nest:
Befotaka-3. Chicks in Befotaka-3 nest were sepa-
rated by a stick fence when observations began on
17 September, 24 d after reintroduction. In addition
to color bands for identification, several physical and

March 1996

Madagascar Fish- Eagle Management

Table 2. Comparison of number of call bouts between older (A) and younger (B) chicks, number of visits by adults
to each chick and the separating fence, number of fish loads brought to each chick by adults, and time spent feeding
by chicks, at Befotaka-3 nest, (nr = not recorded, ? = chick not visible in the nest.)

Date

Obser-
vation _

Call Bouts by
Each Chick

N OF Visits by
Adults to

Each Chick and Fence

Fish Loads
Brought by
Adults to
Each Chick

Time (min)
Spent Feeding
BY Chicks

Time, hr

Fence

Sep 17

7.5

Sep 18

1.0

Sep 24

4.0

101

Sep 25

3.5

Sep 26

4.5

303

Sep 27

4.5

368

Sep 28

12.0

Sep 29

12.0

Sep 30

5.0

Oct 1

5.0

Total

59.0

1053

273

282

behavioral differences were apparent between the
chicks that remained obvious throughout the period
of observation. The older, chick A, had a mass of
1800 g on 23 August at age 33 d and appeared
slightly larger, when observed from a distance, than
chick B which had a mass of 1300 g at age 32 d on
26 August. Chick A had more down remaining on
the underside of its wings, a higher pitched and
louder vocalization than chick B, and its behavior
was always the more aggressive of the two. During
the first 2 d of observation the chicks appeared to
ignore each other. From 24-27 September, chick B
was seen to sit on top of the fence, looking into the
opposite side at its sibling for a total of 3%, 6%, 13%
and 9% of each observation day (Table 2), respec-
tively. On 28 September chick A jumped into chick
B’s side of the nest, while chick B was being fed by
an adult. They remained together on the same side
of the nest until fledging.

Chick A vocalized almost continuously (Table 2)
except immediately after it was fed on 25 September
and after it fed on chick B’s side on 28 September.
Before this occurred, the adults landed on chick B’s
side of the nest four times more often than chick A’s
side (Table 2), and chick B was seen feeding over
twice as long (232 min) as chick A (110 min, Table
2). The number of fish loads brought to chick B’s
side was almost twice that brought to chick A’s side
(Table 2). In contrast, the first 3 d both chicks were

together, chick A fed for 1 63 min while chick B fed
for only 50 min. Up to this point, chick B had hardly
ever vocalized, but on 30 September it called 40 times
before being fed at 0930 H when it stopped calling.

Chicks were observed from dawn to dusk on 28
and 29 September (Table 2) to document behavior
once they were no longer separated by the fence.
When chick A first jumped into chick B’s side of the
nest and began feeding, chick B and the adult simply
looked on. After 2 min, the adult flew from the nest.
The first day together the chicks sparred occasionally
with their bills, but inflicted no wounds. Thereafter,
they fed side by side and coexisted without fighting.
However, chick A usually appeared dominant over
chick B, seizing fish brought to the nest by adults
and feeding first. Chick B never responded aggres-
sively to this behavior; it would circle chick A and
wait to feed on the food remains. Chick B sometimes
fed first, usually during the second or later meal of
the day. Apart from the first night in chick B’s side
together, chick A always settled in the center of the
nest, displacing its sibling to the edge.

Chicks began exercising their wings before 17
September, first flapping in place on the nest, fol-
lowed by sustained flapping above the nest beginning
on 24 and 26 September at 62 and 68 d of age. Both
chicks showed a pattern of exercising frequency in
which exercising on the nest reached a peak 3 d
ahead of aerial flapping while hovering above the

Watson et al.

VoL. 30, No. 1

nest. Chick B reached peak frequency of exercising
in place on 24 September, while chick A reached its
peak on 27 September.

Three different adults regularly visited the nest
and fed chicks. The largest of the adults (assumed
to be female) was colorbanded and wore a tail-
mounted radiotag. The other two adults could not
be distinguished unless seen simultaneously. During
observations, the female spent over twice as much
time at the nest (316 min) as the other two adults
combined (136 min). The female was twice seen to
fly to one of the other adults, take a fish from it and
deliver the fish to the nest. Adults were seen actively
feeding the chicks as well as simply delivering fish
to the nest for the chicks to feed themselves.

Discussion

Siblicide in eagles is either obligate (a chick is
always killed by its sibling) or facultative (mortality
may or may not occur) for each species (Edwards
and Collopy 1983, Mock 1984). Our observations
of breeding attempts by territorial pairs of Mada-
gascar fish-eagles between 1991 and 1994 suggest
the species exhibits siblicide which may be obligate.
In addition, the mass difference between first and
second hatched chicks when the second hatched, and
the growth constant {k = 0.057) for Madagascar
fish-eagle nestlings, are consistent with eagle species
that typically raise only one young {k = 0.024-0.064,
Bortolotti 1986). These observations help justify the
use of sibling rescue as a technique for increasing
annual production in this species.

Once the second egg hatched, it was easier to take
the older chick from the nest first because this min-
imized human involvement in the labor intensive
period of the first 8 d while chicks were feeble and
required most attention. After 8 d, chicks could move
around the brooder on their own and by 12 d they
could pick up food on their own. Given the reaction
to parents of the chick kept for 22 d compared with
that of chicks exchanged each 10 d, swapping ap-
peared to help chicks habituate to parents and may
be important for the success of this method. Ex-
changing siblings after one had been in captivity
about 10 d may have improved the chances of im-
printing on conspecifics.

Introduction of both siblings to the nest once they
appeared capable of thermoregulation and could re-
main separated by a physical barrier worked only
after the nest had been enlarged. The barrier pre-

vented sibling aggression until chicks reached an age
when they were capable of crossing the barrier. By
this time (66 d in Befotaka-3 nest) aggression had
declined sufficiently to allow chicks to coexist in the
same nest. Although dominance by one chick over
the other continued, it was not life-threatening under
the circumstances observed in which adults appeared
capable of providing sufficient food to satisfy both
chicks.

Frequent vocalizing appeared to indicate hunger,
since it dropped to zero immediately after feeding.
Based on observed feeding bouts and vocalization
rate, the motivation for Befotaka-3’s chick A to move
to the chick B’s side of the nest appeared to be
hunger. Chick A was dominant over chick B sub-
sequent to this move. Similar dominance by heavier
siblings has been documented in black eagles (Gar-
gett 1990) that were experimentally placed together
at 10 wk of age and has been recorded in tawny
eagles (Aquila rapax; Steyn 1973) and golden eagles
(A. chrysaetos; Beecham and Kochert 1975) although
aggression in the latter did not cease. Although chick
A was dominant over chick B when together, when
they were separated by the barrier, chick A vocalized
more often but received less food than chick B. The
adult’s stimulus to feed chick B more often was un-
known, but may have been simply the greater ease
of landing on chick B’s side of the nest. Parents
appeared to have no difficulty in feeding both chicks
although parental effort was not measured in this
study. Three adults at one nest have been reported
in bald eagles {Haliaeetus leucocephalus; Sherrod et
al. 1976, Heglund and Reiswig 1980, Fraser et al.
1983), but the high frequency of occurrence seen
among Madagascar fish-eagles seems unusual (Wat-
son et al. 1993).

Using our method, Madagascar fish-eagle chicks
can be reintroduced to their nest by about 4 wk of
age instead of ^9 wk of age when aggression has
diminished. This technique abbreviates the captivity
period and is therefore easier to apply under remote
field conditions of Madagascar than techniques in-
volving lengthy rearing of young chicks. The method
may also be useful in other raptors in which siblicide
is invariably fatal regardless of the chick’s age.

The Madagascar fish-eagles in this study may be
unusual for the amount of human activity and in-
trusion tolerated at and around the nest. Our sub-
jective impression is that the study pairs may be more
tolerant of human intrusion at the nest than pairs
elsewhere in Madagascar that have been subject to

March 1996

Madagascar Fish- Eagle Management

human persecution. This method may not be so
readily applied elsewhere.

Although sibling rescue increased fledging rates,
its use may negatively afifect other critical population
parameters, such as adult survival or fecundity, or
chick A survival to recruitment (Magrath 1991 , Mock
and Forbes 1994). For example, parents raising two
chicks beyond the normal point of brood reduction
may suffer increased mortality or reduced fecundity
in future seasons, or chicks fledging from a two-
chick nest may be less robust and suffer higher mor-
tality between fledging and recruitment to the breed-
ing population. Future attempts at sibling rescue
should measure parental effort and body condition
to look for negative consequences of caring for two-
chick broods. Studies of survival, adult fecundity and
impact on population recovery should be imple-
mented if sibling rescue is adopted as a conservation
tool for this species. It would be beneficial to test
alternative methods for conservation management,
such as sibling rescue followed by hacking in un-
occupied suitable habitat, that do not require inten-
sive intervention at the nest and that minimize pos-
sible negative effects on siblings or parents.

Acknowledgments

This work is dedicated to the memory of Frank G.
Wells. Funding was provided by Environment Now,
Claude Albritton, and the John D. and Catherine T. Mac-
Arthur Foundation. We thank Stefania Strzalkowska, Jules
Mampiandra, and others for valuable field assistance. We
thank the Direction des Eaux et Forets, ANGAP and
UNESCO for collaboration. Ian Newton, Gary Bortolotti,
Douglas Mock, and David Anderson provided valuable
comments on drafts of this paper.

Literature Cited

Beecham, J.J. and M.N. Kochert. 1975. Breeding
biology of golden eagles in southwestern Idaho. Wilson
Bull. 87:506-513.

Bortolotti, G. 1986. Evolution of growth rates in
eagles: sibling competition vs. energy considerations.
Ecology 67:182-194.

Brown, L. 1980. The African fish eagle. Bailey Bros.

and Swinfen Ltd., Folkstone, U.K.

Edwards, T.C., Jr. and M.W. Collopy. 1983. Ob-
ligate and facultative brood reduction in eagles: an
examination of the factors that influence fratricide. Auk
100:630-635.

Fraser, J.D., L.D.Frenzel, J.E. Mathison and M.E.

Shough. 1983. Three adult bald eagles at an active
nest. Raptor Res. 17:29-30.

Gargett, V. 1 990. The black eagle. Acorn Books, South
Africa.

Heglund, P.J. and B. Reiswig. 1980. 1980 raptor

survey, the breeding bald eagle population, Amchitka
Island, Alaska. Unpubl. Rep., USDI Fish Wildl. Serv ,
Aleutian Islands National Wildlife Refuge, AK U.S.A

Langrand, O. AND B.-U. Meyburg. 1989. Range, sta-
tus and biology of the Madagascar sea eagle Haliaeetus
vociferoid.es. Pages 269-278 in B.-U. Meyburg and R.D.
Chancellor [Eds.], Raptors in the modern world. World
Working Group on Birds of Prey, Berlin, Germany.

Magrath, R.D. 1991. Nestling weight and juvenile
survival in the blackbird, Turdus merula. J. Anim. Ecol
60:335-351.

Meyburg, B.-U. 1978. Sibling aggression and cross-

fostering of eagles. Pages 195-200 in S.A. Temple
[Ed.], Endangered birds; management techniques for
preserving threatened species. Univ. Wisconsin Press,
Madison, WI U.S.A.

. 1983. The significance for captive breeding pro-
grammes of fratricide and cainism in birds of prey. Int.
Zoo Yearb. 23:110-113.

Mock, D.W. 1984. Infanticide, siblicide, and avian nest-
ling mortality. Pages 2-30 in G. Hausfater and S.
Blaffer Hardy [Eds.], Infanticide: comparative and
evolutionary perspectives. Aldine, New York, NY
U.S.A.

and L.S. Forbes. 1994. Life-history conse-
quences of avian brood reduction. Auk 111:115-123.

O’Daniel, D. 1995. Raising Cain . . . and Abel. Living
14:30-35.

Sherrod, S.K, C.M. White and F.S.L. Williamson.
1976. Biology of the bald eagle on Amchitka Island,
Alaska. Living Bird 15:143-182.

Steyn, P. 1973. Observations on the tawny eagle. Ostrich
44:1-22.

Watson, R.T and R. Rabarisoa. 1995. Madagascar
fish-eagle offshore survey. Pages 231-239 in R.T.
Watson [Ed.], Madagascar project: wetlands conser-
vation project. Prog. Rep. II, 1993 and 1994. The
Peregrine Fund, Boise, ID U.S.A.

, J. Berkelman, R. Lewis and S. Razafindra-

MANANA. 1993. Conservation studies on the Mada-
gascar fish-eagle Haliaeetus vociferoides. Proc. Pan-Afr
Ornithol. Congr. 8:192-196.

Wilkinson. 1990. SYSTAT: the system for statistics
SYSTAT, Inc., Evanston, IL U.S.A.

Received 9 December 1994; accepted 8 August 1995

Short Communications

J Raptor Res. 30(1):28-31
© 1996 The Raptor Research Foundation, Inc.

The Use of a Power Snare to Capture
Breeding Golden Eagles

M.J. McGrady and J.R. Grant

Royal Society for the Protection of Birds, Scottish Headquarters, 17 Regent Terrace, Edinburgh EH7 5BN, U.K.

Key Words: Aquila chrysaetos; capture techniques', gold-

en eagle', power snare.

Adult golden eagles {Aquila chrysaetos) are difficult to
capture. However, golden eagles of all age classes have
been caught using a variety of methods: Harmata (1985)
used padded-jaw traps, Ellis (1975) used helicopters and
O’Gara and Getz (1986) and S. Brodeur (pers. comm.)
used net guns fired from helicopters, Bloom (1987) used
pit traps, Jackman et al. (1994) used power snares, and
W.S. Clark (pers. comm.) used bow nets.

In western Scotland, where our study took place, it is
illegal to use live lures, winters are mild with little snow
cover, and the eagle population is nonmigratory. This
paper describes a safe, inexpensive, and reliable method
of catching breeding golden eagles without the use of live
lures. It also compares the efficiency of this trap to other
methods and discusses its impact upon the eagles.

Methods and Materials

The trap (Fig. 1) is a modification of a power snare
(Hertog 1987), and the radio-controlled trigger (Fig. 2)
is similar to that described by Jackman et al. (1994). Table
1 lists the parts and their approximate prices.

We used a shock cord 10 m in length and 5 mm in
diameter in most situations, and stretched it to achieve
noose closure with 1-2 kg of tension. The length of elastic
needed was determined by the size of noose to be closed.
The tension was set using a spring balance. The diameter
of the noose could be adapted to the situation, but was
typically 30-35 cm. To close a noose this size our 10 m
elastic was stretched to about 30 m. At the end of the
noose-line, a small (3 mm) eyelet was affixed by tying the
noose around the outside of the eyelet and locking the knot
with Superglue. This ensured that the noose closed quickly
and smoothly.

The trigger mechanism was designed to avoid inadver-
tant firing: the pin which holds the rat-trap armature fits
into a deep sleeve, and the connection between the rat-
trap and the trigger pin is a flexible nylon cord, ensuring
that any vibration at the trigger pin would not be trans-
ferred to the rat trap. The radio controls are sometimes
affected by radio signals from other sources (especially

around harbors) which can fire the trap accidentally, so
radio controls with changeable crystals were used.

To avoid injury, a nest anchor was used to keep the
captured eagle on the nest, but away from the nestling.
This was usually a large (85 cm long) corkscrew with a
sailing cleat attached to the top. The cleat allows the noose-
line to travel only in the direction of the trigger, holding
the noose closed. We sometimes used a nearby tree (<1
m away) as an anchor, nailing the cleat to the tree above
the level of the nest. Otherwise, the cleat can be incor-
porated into the trigger assembly.

Thin wire (4 mm) or bamboo guides are used to ensure
that the closing noose is not fouled by the nesting material,
and help lift the noose around the bird’s tarsi. The tips of
the wires were filed to eliminate sharp points.

Nestlings must be isolated on the nest so that they do
not foul the trap before firing, and are well out of the way
of the captured parent. This can be done either by placing
the nestlings within a small chicken-wire cage or by se-
curing with jesses to a small corkscrew-shaped anchor
(made from 3-4 mm steel wire).

Trapping success and safety were highest when the
operator had a direct view into the nest. At some nests a
video camera facilitated a clear view of the trap.

Results

Eight territorial golden eagles (three males, five females)
were captured during the nestling period in 1992 (1), 1993
(4), and 1994 (3). Both members of one pair were captured.
In all, attempts were made to capture 10 individuals re-
sulting in an 80% capture success. Successful captures were
made having triggered the trap 12 times (75% efficiency).
Capture of individual eagles took between 5 hr and 4 d,
including trap setup and dismantling time.

No decline in productivity or nesting success was de-
tected following capture, and all nestlings fledged. In the
year following capture, all territories at which eagles were
captured were active (nests built up), and five of seven
pairs laid eggs. In the year subsequent to capture success
(x^ ~ 0.16, P >0.05) and productivity {yf = 0.27, P >0.05)
were similar to that within the rest of the study area.

Trapping activities probably caused eagles to shift nests
more often than they would without disturbance. All
trapped eagles used new nests in the year following cap-
ture. In comparison, eagles on these territories changed

March 1996

Short Communications

Corkscrew
Nest Anchor

nests only 47 out of 84 nesting attempts (55.9%) in years
prior to capture.

Discussion

Territorial golden eagles can be caught on the nest
efficiently and safely using the power snare design we
describe. Failures to capture birds were due to the lack of
a clear view into the nest or fouling of the noose on nest
material or prey remains. The age of the nestling also
affected the success of trapping because adults visited older
nestlings less often, and the large nestlings left no room
on the nest for the trap.

No major injury was sustained by any of the captured
eagles. Although one was found to be cut on the abdomen,
this injury may have been sustained at some other time
because the blood surrounding the wound was dry when
it was first noticed. Still, as with any trap, there are dan-
gers, and all efforts must be made to ensure safety. Prevost
and Baker (1984) reported some fatal injuries when trap-
ping ospreys using a similar trap, although it was triggered
automatically. As an additional safety precaution, we would
recommend the use of flattened U-shaped wire guides,
instead of straight ones.

We found no indication that trapping had any long- or
short-term negative effects on the nestlings. No desertions
occurred, and in all cases, the trapped bird revisited the
nest within 24 hr. In two nests video cameras monitored
the post-capture visitation rate by the adults. We were
unable to assess whether captured birds took longer to
return to their nest than those which had not been captured
because of the variability in age of nestlings, weather, and
time of day capture occurred.

The effect the trap had upon the adult’s return to the
nest was difficult to determine. The adults appeared wary,
and sometimes flew past the nest before going onto it.
Initially, the presence of the nest anchor may have caused

the eagles to be reluctant to return to the nest, but one
adult returned in less than 2 hr (although it was not in a
position to be caught). When eaglets were isolated on the
nest using a cage, parents were seen to feed and brood
them through the wire mesh. For large nestlings, restrain-
ing them with jesses allowed them to stand and move about
more freely, and was believed to be less likely to damage
growing feathers. However, A. Harmata (pers. comm )
warns that jesses can cause leg tendon injuries, although
no obvious injuries to eaglets occurred during our trapping
efforts.

It is important that trapping should be conducted only
after the nestlings are able to thermoregulate, and only in

Table 1. Trap and trigger components and approximate
prices.

Trap

Elastic cord

Noose with eyelet

Nest anchor

Cleat

Guides

Anchor

Trigger plate

Radio-controlled trigger
Radio control and servo
Battery

Water resistant box
Nuts, bolts, etc.

S 6.00
0.50
10.00
5.00
nil
nil
nil

60.00

8.00

2.00

5.00

Short Communications

VoL. 30, No. 1

Figure 2. Detail of the radio-controlled trigger mecha-
nism and sailing cleat. When a corkscrew nest anchor is
used, the cleat on the trigger mechanism is not used (See
Fig. 1).

good weather. Activities should be suspended in the hours
prior to sunset to encourage the return of the adult to
brood. Whether successful or not, eaglets should be hand-
fed by the trapper at the end of each trapping session. In
our study area, eagles typically raise only one nestling,
although they hatch two. At one site brood reduction oc-
curred the week after cessation of (unsuccessful) trapping
activities.

Because golden eagles are big, powerful birds, there is
a temptation to set the elastic tension much too strongly.
However, success rate was higher when the tension was
less. When the tension of the elastic was too great, the
whip-like closing of the noose startled the eagle and the
noose fell from its feet as it flushed. A lightly set noose
closed more gently around the legs of the eagle which was
less likely to flush, instead walking around the nest with
the noose around both legs. While walking it usually re-
moved one leg from the noose which then closed around
the other. Experience suggests that as little as 1.2 kg of
tension is needed for golden eagles.

Although this is an efficient method for capturing eagles,
we believe that capture outside the breeding season and
away from the nest is preferable. Before using this method,
one should weigh carefully its potential impact, particu-
larly in areas where the number of nesting places is
limited or where there is a difference in suceess between
nesting places within a territory.

Resumen. — Como parte de un estudio de radiotelemetria
de Aquila chrysaetos, una trampa radio-conrolada fue di-
senada para capturar individuos reproductivos. La unidad
de gatillado incorpora una forma de proteecion que ase-
gura que la trampa no pueda ser activida mas que por el
ave bianco. La efectividad de la trampa fue muy alta (80%),
especialmente cuando el operador tenia una buena vista
del nido (100%). Durante tres estaciones consecutivas, ocho
individuos territoriales fueron capturados (tres machos y
cinco hembras). No hubo abandonos de nidos y tampoco
una reduccion de productividad o exito al ano siguiente
de las capturas. El trampeo causo mas cambios en el sitio
de nidificacion al ano siguiente de las capturas. Por lo
tanto, este metodo puede ser usado solamente cuando mu-
chos lugares de nidificacion igualmente apetecibles estan
disponibles en el territorio. Aunque efectivo, nostros sug-
erimos otros metodos, menos intrusivos, para lo captura
en nido.

[Traduccion de Ivan Lazo]

Acknowledgments

This method was developed during a joint study between
the RSPB and the Forestry Authority under contract num-
ber RD9-4-CON-24. The support of the Argyll Raptor
Study Group as well as that of local enthusiasts, farmers,
forest rangers, landowners and gamekeepers has been in-
valuable. I.P. Bainbridge, S.J. Petty, A.R. Harmata, D.L.
Evans, and R.E. Jackman provided useful comments on
early drafts.

Literature Cited

Bloom, P.H. 1987. Capture and handling raptors. Pages
99-123 in B.A. Pendleton, B.A. Millsap, K.W. Cline,
and D.M. Bird. [Eds.], Raptor management tech-
niques manual. Natl. Wildl. Fed. Sci. Tech. Series 10,
Washington DC U.S.A.

Ellis, D.H. 1975. First experiments with capturing
golden eagles by helicopter. Bird-Banding 46:217-219.

Harmata, A.R. 1985. Capture of wintering and nesting
bald eagles. Pages 139-159 in J.M. Gerrard and T.N.
Ingram. [Eds.], The bald eagle in Canada: proceedings
of bald eagle days. White Horse Plains Publ., Head-
ingly, Manitoba, Canada.

Hertog, A.L. 1 987. A new method to selectively capture
adult territorial sea-eagles. J. Raptor Res. 21:157-159.

Jackman, R.E., W.G. Hunt, D.E. Driscoll and F.J.
Lapsansky. 1994. Refinements to selective trapping

March 1996

Short Communications

techniques: a radio-controlled bow net and power snare Prevost, Y.A. AND J.M. Baker. 1984. A perch snare

for bald and golden eagles. J. Raptor Res. 28:268-273. for catching ospreys. J. Wildl. Manage. 48:991-993

O’Gara, B.W. and D.C. Getz. 1986. Capturing golden

eagles using a helicopter and net gun. Wildl. Soc. Bull. Received 15 July 1994; accepted 15 July 1995
14:400-402.

J. Raptor Res. 30(l):31-32
© 1996 The Raptor Research Foundation, Inc.

A Mechanical Owl as a Trapping Lure for

Raptors

Eugene A. Jacobs

Linwood Springs Research Station, 1601 Brown Deer Lane,
Stevens Point. WI 54481 U.S.A.

Key Words: Bubo virginianus; capture technique, great

horned owl', lure', mechanical owl', mist net.

A live great horned owl {Bubo virginianus) used as a
decoy is an effective method for capturing several species
of breeding raptors (Hamerstrom 1963, Bloom et al. 1992,
Steenhof et al. 1994). Similar techniques were practiced
by Arab and Persian falconers (Meredith 1943). Taxi-
dermy mounts of great horned owls have also been used
successfully to capture breeding raptors, but are not as
effective as a live owl (Bloom 1987). Gard et al. (1989)
reported breeding American kestrels {Falco sparverius) re-
sponded less aggressively to a mounted great horned owl
than to a live owl, suggesting that the lack of movement
or some other subtle cue by the mounted owl may account
for the lower response rate. However, logistics (e.g., weath-
er conditions, remote nest sites, maintenance of owl, legal
constraints) sometimes warrant the use of a mounted owl
as a substitute for a live great horned owl. Here, I describe
the materials used to construct a moving mechanical owl
and compared the results of my trapping efforts with this
lure to other studies using a live and mounted (taxidermic)
great horned owl.

Methods

Materials and Assembly. A two-channel remote con-
trol unit (transmitter, receiver, battery pack, and two servo
mechanisms) designed for a model car was slightly mod-
ified to provide movement to a mounted great horned owl.
The owl’s head and body were separated and mounted
independently using standard taxidermy procedures. The
mechanical owl’s body was attached to a horizontal wood-
en perch (9 cm dia. x 20 cm). A piece of styrofoam was
excised from the body of the mechanical owl at the top
center and fitted with servo A (Fig. 1). Two vertical pins
(3 mm dia. x 10 cm) were glued into the control arm of
servo A and two corresponding sleeves were glued into the

styrofoam head of the mechanical owl. Servo A supported
and provided movement to the mechanical owl’s head
Servo B was placed in a holding bracket constructed of
sheet metal and attached to an aluminum rod (7 mm dia.
X 1 m) used to support the mechanical owl’s perch. In
the underside of the mechanical owl’s perch, I inserted a
copper sleeve (9 mm dia. x 12 cm) into the center and a
pin (4 mm dia. x 1 1 cm) at one end with approximately
half of the pin exposed. To provide movement to the entire
mount, servo B’s control arm was modified with a piece
of tempered wire (3 mm dia. x 30 cm) bent in half and
attached at both ends to the control arm. The mechanical
owl and perch assembly were positioned on top of the
aluminum rod, elevating the owl 1 m above the ground
and allowing rotation of the mount. Servo B provided
movement to the entire mount, allowing the observer to
control movement of the entire mount and the mechanical
owl’s head independently.

Method of Use. From 1989 through 1995, the me-
chanical owl was tested on breeding sharp-shinned hawks
{Accipiter striatus), red-shouldered hawks {Buteo lineatus),
and Cooper’s hawks {Accipiter cooperii). A response was
considered to have occurred when the target species stooped
at least once within 1.5 m of the mechanical owl’s head.
During the nestling stage the mechanical owl was centered
< 1 m from the net, in view of and < 50 m from the nest.
An observer concealed <25 m from the net activated the
owl (via transmitter) when at least one of the adults was
detected near its nest.

Results and Discussion

Overall, the mechanical owl was successful in eliciting
a stoop from 79% (75/95) of the nesting adults. This
response was slightly lower than the 93% Gard et al.
(1989) reported when using a live great horned owl on
American kestrels, but considerably higher than the 33%
they found with a mounted great horned owl. Fifteen of
the 20 adults that did not attack the mechanical owl vo-
calized for >15 min before leaving the area. The remain-

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VoL. 30, No. 1

ing five individuals did not show any aggressive behavior
toward the mechanical owl and left the area after a few
minutes.

While trapping red-shouldered hawks in California,
Bloom et al. (1992) reported a higher capture rate using
a live great horned owl than I experienced using a me-
chanical owl in Wisconsin (Table 1). Of the 13 red-shoul-
dered hawks not captured with my technique, three stooped
at the mechanical owl but escaped after hitting the net.

In general, Bloom et al. (1992) found larger raptors
were more difficult to capture than smaller ones. I expe-
rienced similar results with the mechanical owl on the
three species I tested. The sharp- shinned hawk was the
most aggressive, occasionally hitting the net and escaping
<4 times in <10 min. On six occasions the adult(s) ap-
parently saw the net and avoided it on each stoop. The
mechanical owl and net were then moved a short distance
(<15 m), resulting in four captures.

The mechanical owl was an effective decoy for capturing
these three raptors. Even though attack and capture rates
were slightly lower using the mechanical owl than in stud-
ies using a live great horned owl, I recommend its use
when logistics render the use of a live owl difficult.

Table 1. Comparison of capture rates of a mechanical
owl to a live owl as a trapping lure.

Mechanical

Live Owl

Owl

(Bloom et al.

(This Study)

1992)

Red-shouldered hawk

54% (15 of 28) 75% (199 of 264)

Cooper’s hawk

60% (3 of 5)

52% (32 of 62)

Sharp-skinned hawk

77% (48 of 62)

Resumen. — Un biiho preparado taxidermicamente fue
equipada con mecanismos radio-controlados en la cabeza
y percha que permitian movimientos al buho. Este ingenio
mecanico y una red de niebla fue usada como tecnica de
captura durante siete estaciones reproductivas de tres es-
pecies de rapaces. Este metodo fue exitoso atrayendo a un
79% de adultos reproductivos. Setenta y siete por ciento
de Accipiter striatus, 60% de A. cooperii y 54% de Buteo
lineatus, fueron capturados por este metodo. El movimiento
del buho mecanico parecio ayudar a las especies bianco a
localizarlo y verlo como una amenaza hacia sus juveniles.

[Traduccion de Ivan Lazo]

Acknowledgments

I am grateful to L. Semo, L. Ayers, T. Hoppa, P.
Hnilicka, R. Jacobs, G. Wolf, D. Grosshuesch, S. Braun,
G. Proudfoot, and S. Lind for their field assistance. J.
Runke supplied the drawing in Fig. 1. J. Jacobs, L. Semo,
R. Rosenfield, D. Evans, P. Bloom and P. Schempf pro-
vided helpful comments and suggestions on the manu-
script.

Literature Cited

Bloom, P.H. 1987. Capturing and handling raptors.
Pages 99-123 in B.G. Pendleton, B.A. Millsap, K.W.
Cline and D.A. Bird [Eds.], Raptor management tech-
niques manual. Natl. Wildl. Fed., Washington, DC
U.S.A.

, J.L. Hengkel, E.H. Henckel, J.K. Schmutz,

B. WooDBRiDGE, J.R. Bryan, R.L. Anderson, P.J.
Detrich, T.L. Maechtle, J.O. McKinley, M.D.
McCrary, K. Titus and P.F. Schempf. 1992. The
dho-gaza with great horned owl lure: an analysis of its
effectiveness in capturing raptors. J. Raptor Res. 26.
167-178.

Gard, N.W., D.M. Bird, R. Densmore and M. Hamel.
1989. Responses of breeding American kestrels to live
and mounted great horned owls. /. Raptor Res. 23:99-
102 .

Hamerstrom, F. 1963. The use of great horned owls
in catching marsh hawks. Proc. Int. Ornithol. Congr.
13:866-869.

Meredith, R.L. 1943. Methods, ancient, medieval, and
modern, for the capture of falcons and other birds of
prey. Pages 433-449 in C.A. Wood and F.M. Fyfe
[Eds.], The art of falconry. Stanford Univ. Press, Stan-
ford, CA U.S.A.

Steenhof, K., G.P. Carpenter and J.C. Bednarz.
1994. Use of mist nets and a live great horned owl to
capture breeding American kestrels. J. Raptor Res. 28:
194-196.

® Not given.

Received 14 April 1995; accepted 1 September 1995

March 1996

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J. Raptor Res. 30(l);33-35
© 1996 The Raptor Research Foundation, Inc.

Feeding of the Bat Falcon {Falco rufigularis )

IN AN Urban Environment

Andres E. Seijas

UNELLEZ, Mesa de Cavacas, Guanare, Portuguesa, Venezuela

Key Words: bat falcon; Falco rufigularis; urban

environment; Venezuela.

The bat falcon {Falco rufigularis) inhabits a variety of
forested areas and forest clearings throughout the Neo-
tropical region (Beebe 1950, Haverschmidt 1962, Inigo-
Elias 1993). Beebe (1950) made a detailed analysis of
feeding behavior of a pair of these birds in a mountainous
forest in Venezuela. He found that 16% of the vertebrates
taken by the falcons were bats. Small birds, however,
comprised the bulk (75%) of prey. Additional aspects of
feeding are discussed by several authors (Wetmore 1965,
Brown and Amadon 1968, Kirven 1976, and Chavez-
Ramirez and Enkerlin 1991). The occurrence of bat fal-
cons in urban areas has also been reported. Wetmore (1965)
and Tostain (1986) mentioned them hunting bats and
insects in small towns. However, details on feeding ecology
of this species in urban environments are lacking. In this
paper I analyze prey taken by three bat falcons, a pair
and a juvenile, in an urban environment and compared it
to the data available in the literature.

Study Area and Methods

My observations were made in Guanare, a city of some
100 000 people located in the llanos of Venezuela (9“2'40"
N, 69°44'30"W). The northern part of the city is bordered
by hills and low plateaus covered by forest relicts and
savanna-like vegetation. The rest is mostly surrounded by
savannas and deforested areas dedicated to agriculture and
cattle ranching. The climate of the region is biseasonal,
with a rainy season that extends from May to October,
and a dry season that goes from December to March. April
and November are transitional. The annual precipitation
is 1473 mm and the average annual temperature is 27.1 °C.

My observations began on 4 December 1993 when I
saw one bat falcon perching on the top of the tallest (seven
stories) building in the city. From December 1993 to Feb-
ruary 1994, only one bat falcon was seen at a time. A pair
was rarely seen during March and early April. On April
23 the presence of a third falcon, likely a fledgling of the
pair, was noted. The pair of falcons had nested in another

^ Present address: Department of Wildlife Ecology and
Conservation, University of Florida, Gainesville, FL 32611
U.S.A.

building 200 m from my observation point (M. Gonzalez
pers. comm.). The prey remains left under perches were
collected at irregular intervals between 5 February and
20 July 1994.

Results and Discussion

Remains of 47 vertebrates were found (Table 1). Moths,
grasshoppers, beetles, and butterflies were also occasion-
ally found, but a more precise identification and quanti-
fication of these items was not attempted. The relatively
high number of prey found during May probably reflects
the presence of three falcons. After June the frequency in
which the falcons were seen declined. That may explain
the small number of remains found during that month.

These results confirm the importance of bats as prey of
bat falcons; bats made up almost 64% of the identifiable
vertebrate remains. All bat remains that could be identified
to species were mastiff bats (Molossus molossus). Chase et
al. (1991) calls this bat an almost strictly crepuscular
species whose large colony size and predictable foraging
times makes it particularly vulnerable to hawk predation.

Even though birds comprised a relatively small number
of the prey taken, they represent a high proportion (at
least 73.5%) of the biomass. Some of the birds, as for
example the least bittern {Ixobrychus exilis) and the purple
gallinule {Porphyrula martinica) may be as heavy or heavier
than bat falcons (Karr et al. 1990, ffrench 1991). Capture
of relatively large prey by bat falcons has been mentioned
by Sick (1993) and Chavez-Ramirez and Enkerlin (1991).

Some of the remains found belonged to common birds
in Guanare, e.g., mockingbirds {Mimus gilvus) and ruddy-
ground doves {Columbina talpacoti). Fringillidae remains
were probably those of saffron finchs (Sicalis flaveola), a
species seen frequently in the area. The carib grackle
{Quiscalus lugubris), another very common bird in the city,
was not found in the prey remains even though I saw a
bat falcon unsuccessfully chasing one of those birds. The
most striking finding was the occurrence of aquatic birds
among the prey captured by the falcons. Aquatic birds
represented 35.2% of all bird remains and at least 51.9%
of total vertebrate biomass. No wetlands or bodies of water
occur within the city. Aquatic birds may have been cap-
tured along the Guanare River some 6 km to the southeast.
Foraging by bat falcons in aquatic habitats has been re-
ported (Stiles and Skutch 1990) or may be inferred from
other published or unpublished evidence. Brown and
Amadon (1968) pointed out that bat falcons were a “ter-
ror” to least grebes {Tachybaptus dominicus) in a locality
in El Salvador. Inigo-Elias (1993) found that these raptors

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VoL. 30, No. 1

Table 1. Prey of bat falcons in an urban area of Vene-
zuela. Cumulative weight of prey was calculated taking
the minimum mass value for each species.

Collection Dates ^
CUMU-

Feb- lative

Ru- Prey

Prey ary May June July Mass, g

Bats

330“

Birds

Podicipedidae

Tachybaptus dominicus

250^

Ardeidae

Ixobrychus exilis

80*^

Unidentified

—

80^^

Rallidae

Laterallus exilis

32^>

Porphyrula martinica

—

205‘’

Columbidae

Columbina talpacoti

94b

Dendrocolaptidae

Dendrocincla fuliginosa

37. U

Tyrannidae

Unidentified

Mimidae

Mimus gilvus

49.5

Thraupidae
Thraupis episcopus

30*’

Fringillidae

Oryzoborus angolensis

Unidentified

—

Passeriformes

Unidentified

“ Minimum mass value (11 g) reported by Chase et al. (1991).
Minimum mass values reported by Karr et al. (1990).

were more frequently seen in riparian forest (0-100 m
from the edge of the river) than in any other natural or
disturbed vegetation type in the Lacandon forest. Bat fal-
cons have been seen along riparian forests and large rivers
foraging on aquatic birds, swifts, and swallows (E. Inigo-
Elias (pers. comm.). Kirven (1976) pointed out that one
characteristic of suitable habitat for bat falcons is the pres-
ence of mesic conditions (streams, rivers, ponds). A bat
falcon collected in May 1981 in a wetland area in Ven-
ezuela (Cienagas de Jaun Manuel, Zulia state) had a
stomach full of dragonflies (A. Seijas unpubl. data). Drag-
onflies were often mentioned in the diet of the bat falcon

(Wetmore 1965, Brown and Amadon 1968, Kirven 1976,
Cade 1987, Sick 1993) which may indicate the importance
of aquatic habitat for this species.

The ability of bat falcons for taking and transporting
prey from distant places was mentioned by Beebe (1950),
but those prey were mostly small Passeriformes and Apod-
iformes. Chavez-Ramirez and Enkerlin (1991) also sug-
gested that bat falcons hunted far from the perch where
they were usually seen.

These results highlight the ecological plasticity of the
bat falcon in the wide variety of habitats used and the
wide spectrum of animals this falcon preys upon. The
importance of aquatic prey, however, had not been em-
phasized in previous reports.

Resumen. — Se identificaron los restos de presas dejados
por tres Halcones Golondrina {Falco rufigularis) bajo sus
perchas en un edificio centrico de la ciudad de Guanare,
Venezuela. Se recolectaron restos de un total de 47 ver-
tebrados. Los murcielagos representaron el 64% de las
presas, el resto pertenecia a diversas aves. Al considerar
el peso de las presas, las aves conformaron no menos del
73.5% del peso total de los vertebrados capturados. Se
identificaron seis aves acuaticas, pertenecientes al menos
a 4 diferentes especies. Las aves acuaticas representaron
el 51.9% de la biomasa total. Estas aves deben haber sido
capturadas fuera de la ciudad, ya que no existen humedales
dentro de sus limites.

[Traduccion Autore]

Acknowledgments

I thank Antonio Utrera and Manuel Gonzalez for their
help in identifying prey remains. Eduardo Inigo-Elias and
Eduardo Alvarez and three anonymous referees made
valuable comments on the manuscript and provided im-
portant references.

Literature Cited

Beebe, W. 1950. Home life of the bat falcon, Falco
albigularis albigularis Daudin. Zoologica 35:69-86.
Brown, L. and D. Amadon. 1968. Eagles, hawks and
falcons of the world. Vol. 2. McGraw-Hill Book Co.
New York, NY U.S.A.

Cade, T.J. 1987. The falcons of the world. Cornell
Univ. Press. Ithaca, NY U.S.A.

Chase, J., M. Yepes, E.A. Weiss, D. Sharma and S.
Sharma. 1991. Crepuscular activity of mo-

lossus. J. Mammal. 72:414-418.

Chavez-Ramirez, F. and E.C. Enkerlin. 1991. Notes
on the food habits of the bat falcon {Falco rufigularis)
in Tamaulipas, Mexico. /. Raptor Res. 25:142-143.
ffrench, R. 1991. A guide to the birds of Trinidad and
Tobago. Comstock Publ. Assoc., New York, NY U.S.A.
HaversCHMIDT, F. 1962. Notes on the feeding habits
and food of some hawks of Surinam. Condor 64:154-
158.

I^IGO-Elias, E.E. 1993. Habitat use and relative abun-
dance of bat falcon in the Selva Lacandona region of
Chiapas, Mexico. J. Raptor Res. 27:73-74.

March 1996

Short Communications

Karr, J.R., S. Robinson, J.G. Blake and R. Bier-
REGAARD, Jr. 1990. Birds of four neotropical forests.
Pages 237-272 in A.H. Gentry [Ed.], Four neotropical
rainforests. Yale Univ. Press, New Haven, CN U.S.A.
Kirven, M.N. 1976. The ecology and behavior of the
bat falcon, Falco rufigularis. Ph.D. dissertation, Univ.
Colorado, Boulder, CO U.S.A.

Sick, H. 1993. Birds in Brazil. Princeton Univ. Press,
Princeton, NJ U.S.A.

Stiles, G. AND A.F. Skutch. 1990. A guide to the birds
of Costa Rica. Cornell Univ. Press, Ithaca, NY U.S.A.

Tost AIN, O. 1986. Adaptation du mode de chasse chez
le faucon des chauves-souris {Falco rufigularis) en Guy-
ane. Alauda 54:66-67.

Wetmore, a. 1965. The birds of the Republic of Pan-
ama. Part 1. Tinamidae (Tinamous) to Rynchopidae
(Skimmers). Smithsonian Misc. Coll. Vol. 150. Wash-
ington, DC U.S.A.

Received 10 April 1995; accepted 18 August 1995

Estimating Age Classes in King Vultures
(Sarcoramphus papa) Using Plumage Coloration

Jack Clinton Eitniear

Center for the Study of Tropical Birds, Inc., 218 Conway Drive,
San Antonio, TX 78209-1716 U.S.A.

Key Words: ageing; king vulture; plumage coloration;

plumage maturation.

Researchers conducting field studies on sexually mono-
morphic vultures have utilized molt and plumage char-
acteristics to identify individuals (Snyder et al. 1987, Wal-
lace and Temple 1987). Such characteristics are valuable
in determining age classes needed to detail survivorship
patterns (Todd and Gale 1970). No reliable criteria are
known for age class determination in king vultures {Sar-
coramphus papa). Wallace and Temple (1987) distin-
guished six age classes in this species, but they failed to
describe which plumage characters they considered. Ad-
ditionally, Heck (1968) provided scant details of plumage
color patterns with no discussion of 5 and 6 yr age classes.
In order to determine reliable criteria for age determi-
nation in the wild, I examined known-age king vultures
in captivity, and documented gross plumage coloration.
For a detailed description of the definitive plumage col-
oration in king vultures, consult Friedmann (1950). A
description of natal downs is detailed by Ramo and Busto
(1988) and Schlee (1994).

Methods

Twenty-seven photographs of 16 known-age birds (four
males, four females) and eight of unknown sex were taken
as follows: three photographs of 1-yr olds, nine of 2-yr
olds, five of 3-yr olds, three of 4-yr olds, four of 5-yr olds,
two of 6-yr olds, and one of a 7-yr old. Individual birds

were photographed from one to five times. Five birds were
permanently housed outdoors in San Antonio, Texas. The
remaining 11 were maintained at the Detroit Zoological
Garden in Detroit, Michigan. The birds in Detroit were
exhibited outdoors during the summer months and housed
indoors under artificial lighting during the winter months
(T. Schneider pers. comm.). Only feathers that change
from black to white with maturity were considered: the
interscapular and dorsal regions of the spinal tract, ventral
tract, and under-tail coverts of the caudal tract. Also con-
sidered were the white alar-tract feathers including the
seven upper middle coverts, carpal coverts, and all under-
wing coverts. The final region changing from black to
white includes the feathers of the femoral and crural tracts
(Fisher 1943).

Results and Discussion

Five age categories were tentatively distinguished by
plumage coloration in captive birds (Table 1) that were
consistent with descriptions by Nuttall (1832), Dickey and
van Rossem (1938), and Heck (1968). The categories con-
flict with statements by Brown and Amadon (1968) who
indicate that second-year birds have all white underparts
and third-year birds are in definitive plumage except for
some black in the inter scapular region. My findings also
are inconsistent with Ruschi (1979) who stated that adult
plumage is attained in the second year of life.

Throughout the first year, all contour feathers including
retrices and remiges are sooty black (Fig. 1). White down
feathers on the femoral and crural tracts can also be con-
sidered characteristic of this stage. During the bird’s sec-
ond year flecks of white begin to appear on the femoral.

Short Communications

VoL. 30, No. 1

March 1996

Short Communications

Table 1. Plumage color criteria for estimating age classes in king vultures.

Age, yr Coloration Characteristics

1- 2 Sooty black coloration with downy feathers observable on femoral and crural tracts

2- 3 Ventral tract with varying amounts of white

3- 5 Ventral tract feathers white; white feathers of alar tract less than 50% white

5- 7 Specks of black remain in lesser wing coverts of alar tract

6- >7 White feathering includes; interscapular and dorsal regions of spinal tract, ventral tract and underwing

coverts of caudal tract. Seven middle upper coverts, carpal coverts, and all underwing coverts as well as
all feathers of the femoral and crural tracts

ventral, and crural tracts. Although the number of third-
year birds observed was limited to four, in all cases at least
50% of the ventral, femoral, and crural tracks became
white. During the fourth year, coloration resembled the
third year with ventral, femoral, and crural tract feathers
white. At this age the alar tract region, e.g., upper wing
coverts {N = 3), also was <50% white. A mottled ap-
pearance, due to the intermixing of white feathers on the
interscapular area of the spinal tract and alar tracts, oc-
curred in 75% (N = 4) of fifth-year birds. One individual
obtained this mottled appearance in its fourth year. Of the
three birds in their sixth or seventh year, only one had
reached definitive plumage (a sixth-year individual). The
other two retained specks of black in the upper wing
coverts.

In addition to the small number of specimens examined,
several additional considerations should be made in eval-
uating the aforementioned data and conclusions. First,
given that only 50% of the individuals examined were of
known sex, no conclusions could be drawn regarding the
possible variation due to sex alone. Such an influence has
not been determined in other monomorphic species that
require long periods for plumage maturation (Jollie 1947,
Palmer 1988, Snyder 1988). Hence, it is unlikely that it
would prove so with this species. Additionally, while king
vultures maintained in Texas were within the photoperiod
and temperature likely experienced by wild birds, the 1 1
maintained in Detroit were not housed under such natural
conditions. It should be noted, however, that previous stud-
ies on king vulture development were conducted with birds
in captivity in north-temperate-zone environments (Heck
1968, Schlee 1994). Secondly, no published account exists
on the annual molt cycle in king vultures. Dickey and van
Rossem (1938) state that the species goes through an an-
nual molt in August. Contrary to this, five captive birds
that I maintained molted throughout the year (Eitniear
unpubl. data). Without knowing the molt cycle, correlating
feather replacement with age appears tenuous.

Using a captive bird, Todd and Gale (1970) determined
that the California condor {Gymnogyps californianus) pri-
mary molt requires 2 yr, and Koford (l953) indicated that
a complete body-feather molt requires more than 1 yr in
the California condor. To prevent excessive loss of flight

efficiency (Tucker 1991), it is likely that the king vulture
requires a similar period of time. In addition, significant
variability in predefinitive feathering tends to hamper as-
signing chronological age or plumage reliably to individual
king vultures. Such variability is common in birds re-
quiring a lengthy period for maturation. Wilbur (1975)
and Snyder (1968) noted that too much variation in plum-
age color exists within age cohorts of California condors
to permit precise age determination of them. Wilbur did,
however, suggest age categories of 1-3 yr (immatures), 3-
4 yr (ringnecks), and 4-5 yr (subadults). He further sug-
gested that first-year birds be aged based upon behavior
and locality (Wilbur 1975). This situation is similar to
that described by Palmer (1988) in bald eagles {Haliaeetus
leucocephalus) as well as in golden eagles {Aquila chrysaetos;
Jollie 1947), and northern goshawks (Accipiter gentilis;
Sushkin 1928). Additional information on king vulture
molt might provide some additional characters, e.g., stage
of molting and feather shape that could augment coloration
in age class determination. Until further information be-
comes available detailing the molt cycle in king vultures,
the utility of using only plumage color characters as re-
liable aging criteria is limited.

ResumeN- — Se investigo el posible uso de criterios de cam-
bios en el color del plumaje para estimar la edad de Car-
roiiero Rey {Sarcoramphus papa). El analisis de 27 foto-
graphias representando a 16 indivuos a diversas edades,
indica que se distinguir cinco categories de edad. El primer
ano se puede diagnosticar por la presencia de plum6n. Las
aves de dos anos empiezan a mostrar coloracibn blanca en
las areas ventrales. Este reemplazo de plumas negras por
blancas continua hasta que las aves alcanzan cuatro anos
de edad cuando tienen un aspecto moteado resultado de
una matrix de plumas blancas y negras en el dorso. La
etapa final de maduracion del plumaje ocurre a los seis o
siete anos de edad cuando las “manchas” de negro en las
coberteras superiores del ala son finalmente reemplazadas
por plumas blancas. Se expresa cierta reserva en la con-
fiabilidad de los criterios de color ya que existe una gran
variabilidad en esta como en otras especies con periodos
de madurez prolongados.

[Traduccibn de Ernesto Enkerlin]

Figure 1. Age estimations based on plumage color development in king vultures. A. 1-2 yr, B. 2-3 yr, C. 3-4 yr,
D. 4-5 yr, E. 6-7 yr, F. 7-8 yr.

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VoL. 30, No. 1

Acknowledgments

I wish to thank T. Schneider (Detroit Zoo) for access
to king vultures under his care. The manuscript benefited
greatly from the comments of J. Baccus, N. Snyder, S.R.
Wilbur, M. Schlee, and C. Thompson. E. Enkerlin pro-
vided the Spanish summary.

Literature Cited

Brown L. and D. Amadon. 1968. Eagles, hawks and
falcons of the world. Vol. 1. Country Life Books, Fel-
tham, U.K.

Dickey, D.R. and A.J. van Rossem. 1938. The birds
of El Salvador. Field Mus. Nat. Hist. Zool. Ser. No.
23. Chicago, IL U.S.A.

Fisher, H.I. 1943. The pterylosis of the king vulture.
Condor 45:69-73.

Friedmann, H . 1950. Birds of N orth and Middle Amer-
ica. U.S. Natl. Mus., Vol. II. Bull. 50, Washington,
DC U.S.A.

Heck, H. 1968. About the plumage of a captive-bred
and raised king vulture {Sarcoramphus papa [L.]). Zool.
Gart. 35:314.

JOLLIE, M. 1947. Plumage changes in the golden eagle.
Auk 64:549-576.

Koford, C.B. 1953. The California condor. Natl. Au-
dubon Soc., Res. Rep. No. 4. New York, NY U.S.A.
Nuttall, T. 1832. A manual of the ornithology of the
United States and of Canada. Hilliard and Brown,
Cambridge, MA U.S.A.

Palmer, R.S. 1988. Handbook of North American birds.
Vol. IV, Part 1. Yale Univ. Press, New Haven, CT
U.S.A.

Ramo, C. and B. Busto. 1988. Observations at a king
vulture (Sarcoramphus papa) nest in Venezuela. Auk
105:195-196.

Ruschi, a. 1979. Aves do Brasil. Editora Rios, Sao
Paulo, Brazil.

Schlee, M.A. 1994. Reproductive biology in king vul-
tures Sarcoramphus papa at the Paris Menagerie. Int.
Zoo Yearb. 33:159-175.

Snyder, N.F.R. 1988. California condor Gymnogyps
californianus. Pages 43-66 in R. Palmer [Ed.], Hand-
book of North American birds. Vol. IV, Part 1. Yale
Univ. Press, New Haven, CT U.S.A.

Sushkin, P.P. 1928. Notes on systematics and distri-
bution of certain Palearctic birds: second contribution.
Proc. Boston Soc. Nat. Hist. 39:1-32.

Todd, F.S. and N.B. Gale. 1970. Further notes on the
California condor at the Los Angeles Zoo. Int. Zoo
Yearb. 10:15-17.

Tucker, V.A. 1991 . The effect of molting on the gliding
performance of the Harris’ hawk {Parabuteo unicinc-
tus). Auk 108:108-113.

Wallace, M. and S. Temple. 1987. Competitive in-
teractions within and between species in a guild of
avian scavengers. Auk 104:290-295.

Wilbur, S.R. 1975. California condor plumage and molt
as field study aids. Calif. Fish Game 61:144-148.

Received 27 April 1995; accepted 19 August 1995

Bigamy in Red-tailed Hawks in
Southwestern Yukon

Frank I. Doyle

Kluane Lake Research Station, Mile 1054 Alaska Highway,
Yukon Territory, Y1A 3V4 Canada

Key Words: bigamy; Buteo jamaicensis; hare cycle;

plumage pattern; red-tailed hawk; Yukon.

Polygyny is well documented in some raptor species
(Newton 1979), and is usually associated with an abun-
dant food supply as seen in hen harrier {Circus cyaneus)
populations in Orkney (Balfour 1962), and common buz-
zard {Buteo buteo) populations in Scotland (Picozzi and

Weir 1974). In red-tailed hawks {Buteo jamaicensis) , only
two cases of polygyny have been reported (Wiley 1975,
Santana et al. 1986). In both cases two females shared the
same mate and nest, but no information on food availability
was available.

Here I describe three incidents of bigamy in a red-tailed
hawk population. In these incidents a male was mated
with two females at different nests, during years of de-
clining prey abundance.

March 1996

Short Communications

Observations

The raptor community at Kluane Lake in the south-
western Yukon has been studied since 1986, as part of a
larger project examining the boreal forest ecosystem (Krebs
et al. 1986, 1992, Boutin et al. 1995). A total of 380 raptor
territories of nine species, including 75 red-tailed hawk
territories, have been closely monitored.

The ability to identify individuals by their plumage
patterns helped me to realize that bigamy was occurring
in this red-tailed hawk population. Light- and dark-phase
birds in this population allowed identification of individ-
uals by plumage characteristics. Of 127 birds for which
plumage charts were made from 1990-94, 58-85% were
individually distinguishable from any other bird within a
year.

Another characteristic helpful in identifying possible
cases of bigamy was the nearest-neighbor nest distance.
Bigamous nests were much closer together (750-800 m)
than were monogamous nests (1400-3500 m; Welch’s ap-
proximate ^-test, P = 0.0000) within years and over the
entire study period.

In 1992, two territories contained males paired with
two females at different nests. At these sites, individually
distinguishable plumage patterns were particularly useful.
In the first territory, the nests were 750 m apart, and in
sight of each other. The first nest discovered (nest #1) had
been used previously and was checked on 9 May. At this
time, the male was seen bringing food to a female on the
nest. Nest #2 was found on 9 June, when the female was
flushed from the nest. She was then joined by a male from
the direction of the nest #1, who had the same plumage
pattern as the male at nest #1. On 19 June, nest #2
contained two young. The view from the nest allowed me
to see nest #1, and the male again flew from that direction
and joined the female circling nest #2. He then returned
to nest #1 where the other female could be heard begging.
On 23 June, nest #2 was empty and great horned owl
{Bubo virginianus) predation was suspected. A large clump
of adult red-tailed hawk and great horned owl feathers
was found at the base of the nest. The first nest fledged
two young, and when checked on 22 June, the female from
the failed nest joined the pair circling above the nest. Over
600 nest visits have been made to red-tailed hawk nests
in the last 7 yr, and only on this occasion did more than
two adults defend a nest.

The other two cases of bigamy were more circumstan-
tial. In the second territory in 1992, the two nests were
also 750 m apart. One nest (nest #1) has been used four
times in the previous 5 yr. On 28 April a female (light-
phase bird) was seen sitting in the nest, while the male
perched 50 ra away. Weekly checks showed both male and
female to be present consistently. On 25 May, the female
was off the nest and begging, and regular checks showed
that she had lost interest in the nest. When the nest was
checked on 27 May it was not defended by the adults, and
it contained two cold eggs. The second nest (nest #2) was
discovered on 20 May when incessant begging from a
female (dark-phase bird) drew me to it. A minute after I
was discovered, the adult female was joined in nest defense
by a male. He flew in from the direction of nest #1, and
had the distinctive plumage pattern of the male at nest

#1. The female at nest #2 was regularly heard begging
from the nest for the next week. A check on 1 1 June found
no adults present. I was unable to see inside the nest, and
no birds were seen here for the remainder of that season.
It is unlikely that young had already fledged, as red-tailed
hawks in our area typically fledge in mid-July.

In 1991, two nests were discovered 800 m apart in a
natural area of patchwork forest and meadow. On 19 June,
one nest (nest #1), contained two healthy chicks and on
23 June the other nest (nest #2) contained one under-
weight chick. Nest checks were made every 2-3 d from
hatching until the young fledged. A nest check was always
made at nest #1 first and the male always appeared quick-
ly and defended the nest. Nest #2 was visited next, and
the male was consistently slow to defend or did not appear
at the nest. When he did appear, the male always arrived
from the direction of nest #1. On two occasions we then
revisited nest #1 after nest #2 had been checked, and both
times the male appeared from the direction of nest #2.
On 8 July, the single chick in nest #2 was found freshly
dead in the nest. There was no sign of predation and the
chick weighed 17% less than the least mass of chicks {N
= 19) of the same age, suggesting it had starved. (Chicks
were aged using the growth pattern of the 4th primary
[Peterson and Thompson 1977]). Both young fledged at
nest #1.

Discussion

In the two cases where bigamy has been previously
documented in red-tailed hawks (Wiley 1975, Santana et
al. 1986), two females shared the same nest, brooded and
fed the young, and both females and the male defended
the nest. Bigamy has been seen in the closely related com-
mon buzzard in Scotland (Picozzi and Weir 1974), where
males were paired with two females at different nests in
five out of 135 territories monitored from 1969-72. In the
Scotland study, and in another report of bigamy in buz-
zards (Newton 1979), bigamy was associated with abun-
dant food supply. This association with an abundant food
supply was not obvious in our study area. An apparent
peak in food availability occurred at the height of the
snowshoe hare (Lepus americanus) cycle in 1989-90 (Bou-
tin et al. 1995). However, bigamy in red-tailed hawks was
only observed in 1991 and 1992.

Variations in fledging success may have been the trigger
for bigamy in our population. During the period of greatest
food supply at the peak of the hare cycle in 1989 and
1990, a peak in fledging success occurred with a mean of
1.75 (SD = 1.12) chicks fledged from 20 pairs. At the hare
low in 1991 and 1992, only 0.76 (SD = 0.88) chicks were
fledged per pair. This 1989-90 high in fledging success
may have caused an increase in the number of birds in
breeding condition over the next few years. Therefore, the
incidence of bigamy in 1991 and 1992 may have been due
to unpaired females joining an established pair rather than
not breeding at all.

Bigamy described here may also be a feature of the
northern location. The birds have a short breeding season
after migration. Nest building and egg laying begin almost
immediately after arrival in mid-April, with a median egg
laying date of 28 April. The birds, therefore, have little
time to assess the quality of the territory or their mate. A

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VoL. 30, No. 1

female could mate with a male who already has a mate,
either by accident or before the quality of the territory is
known.

Whatever the reason for bigamy, 67% of the bigamous
red-tailed hawk nests failed to fledge young. All three
territories failed to fledge young from both nests, and in
one case, both nests failed. These rates are similar to the
monogamous pairs’ breeding success where 55% of 22 nests
failed to fledge any young in the low of the hare population
cycle in 1991 and 1992. Bigamy in this red-tailed hawk
population may be successful only with an abundant food
supply.

Resumen. — Solo en dos ocasiones se han registrado casos
de bigamia para Buteo jamaicensis, en ambos, un macho
estaba emparejado con dos hembras en el mismo nido.
Aqui reporto tres casos de bigamia, donde un macho se
emparejo con dos hembras en nidos diferentes. Estos fueron
observados mientras se monitoreaban 78 intentos de ni-
dificacion en seis anos. Las parejas bigamas se encontraban
mas cercanas entre si (750-800) que parejas monogamas
(1400-3500). La incidencia de bigamia ocurrio en anos
de baja abundancia de presa.

[Traduccion de Ivan Lazo]

Acknowledgments

This study is part of a larger project examining the
snowshoe hare population cycle and its relationship to the
boreal forest ecosystem, funded by the Natural Sciences
and Engineering Research Council of Canada. I received
helpful suggestions with the manuscript from J.N.M.
Smith, M. O’Donoghue and C.L. Doyle. Special thanks
for help with the fieldwork to Tamie Hucal, Shawna
Pelech and Troy Wellicome.

Literature Cited

Balfour, E. 1962. The nest and eggs of the hen harrier
in Orkney. Bird Notes 30:69-73, 145-52.

Boutin, S., C.J. Krebs, R. Boonstra, M.R.T. Dale,

S. J. Hannon, K. Martin, A.R.E. Sinclair, J.N.M.
Smith, R. Turkington, M. Blower, A. Byrom, F.I.
Doyle, C. Doyle, D.S. Hik, L. Hofer, A. Hubbs,

T. Karels, D.L. Murray, V.O. Nams, M.
O’Donoghue, C. Rohner and S. Schweiger. 1995.
Population changes of the vertebrate community dur-
ing a snowshoe hare cycle in Canada’s boreal forest.
Oikos. In press.

Krebs, C.J., B.S. Gilbert, S. Boutin, A.R.E. Sinclair
AND J.N.M. Smith. 1986. Population biology of
snowshoe hares. 1. Demography of food-supplemented
populations in the southern Yukon, 1976-84. /. Amm
Ecol. 55:963-982.

, R. Boonstra, S. Boutin, M.R.T. Dale, S.J.

Hannon, K. Martin, A.R.E. Sinclair, R. Tur-
kington AND J.N.M. Smith. 1992. What drives the
snowshoe hare cycle in Canada’s Yukon? Pages 886-
896 in D. McCullough and R. Barrett [Eds.], Wildlife
2001: populations. Elsevier, London, U.K.

Newton, I. 1979. Population ecology of raptors. T. &
A.D. Poyser, Berkhamsted, U.K,

Peterson, L.R. and D.R. Thompson. 1977. Aging
nestling raptors by 4th-primary measurements. /. Wildl.
Manage. 41:587-590.

Picozzi, N. AND D.N. Weir. 1974. Breeding biology of
the buzzard in Speyside. Br. Birds 67:199-210.
Santana, E.C., R.L. Knight and S.A. Temple. 1986.
Parental care at a red-tailed hawk nest tended by three
adults. Condor 88:109-110.

Wiley, J.W. 1975. Three adult red-tailed hawks tend-
ing a nest. Condor 77:480-482.

Received 24 January 1995; accepted 25 August 1995

J Raptor Res. 30(1):41

Letters

Barred Owl Nest in a Natural Hole in an
Earthen Bank in Eastern Texas

The barred owl {Strix varia) typically nests in old stick nests constructed by hawks, crows, or squirrels, but also in
tree cavities (A.C. Bent 1938, Life histories of North American birds of prey, Part II, U.S. Natl. Mus., Washington,
DC U.S.A.; P.A. Johnsgard 1988, North American owls, Smithsonian Inst. Press, Washington DC U.S. A.). A few
records of nesting sites used by this owl depart from the usual. For example, there is an account of a nest on the
ground in a small hollow dug by a barred owl (H. Mikkola 1973, page 125 in J.A. Burton [Ed.], Owls of the world,
Peter Lowe Publ. Co., London, U.K.). Gibbs (1988, Oriole 53:11) described a nest under a bridge in South Carolina,
and Peterson (1988, pages 206-207 in R.F. Andrle and J.R. Carroll [Eds.], Barred owl, Strix varia. The atlas of
breeding birds in New York state, Cornell Univ. Press, Ithaca NY U.S. A.) noted that this owl will nest in barns.
Johnson and Follen (1984, Raptor Res. 18:34-35) reported barred owls nesting in boxes constructed for them in
Minnesota. However, we found no records of this species nesting in a hole in an earthen bank or cliff.

While walking down Crawford Creek near Appleby, Texas, during the last week of March 1990, FE saw an
unidentified owl fly from a hole in the side of a steep bank on two occasions. The forested area below the bank was
a typical hardwood creek bottom with many mature trees, mostly oaks (Quercus spp.) and sweetgum (Liquidambar
styracijiua) , while the area above the bank was mostly loblolly pine (Pinus taeda) forest. Suspecting the possibility of
a nest, FE rappeled down the sheer vertical face of this 20 m bank and discovered nestling owls in the back of the
hole. The circular entrance to the hole was about 10 m above the creek bed, measured about 1 m in diameter, and
extended horizontally into the bank for about 1 m. Later that week, CS and C.D. Fisher visited the site to identify
the species of owl nesting in the bank. Two 10-d-old nestlings were identified by CS as barred owls.

The hole was an arroyo pipe (Bloom, 1991, Geomorphology, Prentice Hall, Englewood Cliffs, NJ U.S. A.). These
natural pipes are fairly common in the Carrizo sandstones of eastern Texas (R.L. Nielson pers. comm.), and are
formed by the action of water seeping vertically down the sand layers within the hill until it hits an impermeable layer
of clay. The water then flows horizontally along this layer of clay until it eventually exits the hill producing an arroyo
pipe. Through time, the hole becomes larger with the action of flowing water.

We visited the nest hole about 1 wk later after heavy rains in the area to find that the nestlings were not present
in the hole. We suspected that the rainwater washed away the entire contents of the nest since the pipe appeared
smoother, cleaner, and a little larger. If these arroyo pipes are used by nesting barred owls, a relatively flood-free
period of about 6 wk must occur for the nesting attempt to be a success.

We appreciate the information provided on arroyo pipes by R.L. Nielson and we thank D.C. Rudolph and D. Saenz
for constructive comments on an earlier draft of this letter. — Clifford E. Shackelford, Wildlife Habitat and Silvi-
culture Laboratory, Southern Research Station, USDA Forest Service, Nacogdoches, TX 75962 U.S.A.; Frederick
C. Earley, Law Environmental, Inc., Houston, TX 77040 U.S.A.

Unusual Interaction Between Wolf and
Short-toed Eagle

A pair of wolves (Canis lupus) with six pups was observed in the Great Indian Bustard Sanctuary, Nannaj (71°4TN,
75°56'E; altitude 486 m) in Solapur District of Maharashtra State, India. On 16 February 1994 at 0730 H the pair
brought a road-killed female blackbuck {Antilope cervicapra) near their den where they were joined by three of the
pups. The blackbuck was fully grown with a mass of about 30 kg. At 0800 H an adult short-toed eagle {Circaetus
gallicus) soared above them and then perched on top of a tree close to the carcass. The eagle swooped at the wolves
five times either attempting to reach the kill or to attack the pups which were about 5 kg in mass.

Letters

VoL. 30, No. 1

During each swoop the adult male wolf jumped up at the eagle. On the fifth sortie the eagle swooped much lower
and was eaught and killed by the wolf, but was not eaten. The male wolf resumed feeding on the blackbuck carcass
and the pack abandoned the carcass around 1000 H, ignoring the dead eagle.

Interactions between raptors and wolves have been rarely reported (L.D. Mech 1970, The wolf. The ecology and
behavior of an endangered species. Doubleday, New York, NY U.S.A.). Several reports involve interactions between
wolves and common ravens (Corvus corax') since they often feed on the same carcasses (R.O. Peterson 1977, Wolf
ecology and prey relationships on Isle Royale. U.S. Natl. Park Serv. Sci. Monogr. Ser. No. 11.). Ravens irritate wolves
by swooping low over their heads and landing nearby (L. Crisler 1958, Arctic wildlife. Harper and Row, New York,
NY U.S. A.; L.D. Mech 1966, The wolves of Isle Royale. U.S. Natl. Park Serv. Ser. No. 7). Wolves, in turn, leap at
ravens in the air, stalk them on the ground, and scatter them from kills. I have also seen wolves chase crows {Corvus
spp.) from their kills in a similar way. During Isle Royale wolf studies, a wolf was observed catching and killing a
raven (Peterson 1977). The wolves played with the carcass of the raven for 15 min and did not eat it.

This is the first record that I am aware of of a short-toed eagle trying to scavenge a predator’s kill or attack its
young. This eagle is not reported to be a scavenger in the existing literature. The short-toed eagle is reported to feed
mainly on snakes, and secondarily on lizards, amphibia, mice, and other mammals (to hare size), and birds as large
as guineafowl (S. Ali and S.D. Ripley 1987, Handbook of the birds of India and Pakistan, Oxford Univ. Press,
Bombay, India; T.J. Roberts 1991, The birds of Pakistan. Vol. 1, Oxford Univ. Press, Karachi, Pakistan).

This study was funded by the U.S. Fish and Wildlife Service under the Grassland Ecology Project of the Bombay
Natural History Society. We thank Rishad Naoroji of the Birds of Prey Project, Y.N. Rao, Asad R. Rahmani, and
Vibhu Prakash for their constructive comments. — Satish Kumar, Bombay Natural History Society, Hornbill House,
Shaheed Bhagat Singh Road, Bombay 400 023, India.

The Use of a Rock by an Osprey in an
Agonistic Encounter

Whereas many birds manipulate material to build nests, and some use tools to procure food (H.B. Lovell 1958,
Wilson Bull, 70:280-281; G.C. Millikan and R.I. Bowman 1967, Living Bird 6:23-41; J. Boswell 1977, Avic. Mag.
83:88-97), it is unusual to observe a bird using an object in an aggressive encounter. I report the use of a rock in an
agonistic encounter by a male osprey (Pandion haliaetus).

I observed the rock-dropping incident close to an active osprey nest in Stonington, Connecticut on 8 July 1989. The
nest was located in a salt-water marsh to the west of Wilcox Point and adjacent to Long Island Sound and Quiambaug
Cove. A railroad track passed within approximately 100 m of the nest and a series of utility poles ran along the side
of the railroad bed. I observed the nest from 1310-1710 H on 8 July 1989 with a 15-45 x telescope and 9 x 35
binoculars (see J.P. Roche 1995, Conn. Warbler 15:74-77). I was approximately 200 m from the nest and 100 m from
the site where the tool was used.

At 1438 H the female osprey began giving alarm calls (A.F. Poole 1989, Ospreys, Cambridge Univ. Press, Cambridge,
U.K.) from the nest as one male osprey flew into the nest area, followed shortly by three more males. The second male
to enter the area (osprey A) was carrying a partly-eaten alewife (Alosa pseudoharengus). During the next 22 min, the
number of males in the nest area fluctuated between two and four; throughout this period these males behaved
aggressively toward each other.

At 1456 H osprey A flew to a pole along the railroad bed and perched. Next, another male (osprey B) flew to the
ground, picked up a small rock in its talons from the railroad bed, flew approximately 1 m above osprey A, and
dropped the rock on osprey A. Osprey A, which appeared startled but unhurt, flew down to the ground immediately.
Osprey A then flew to another pole and perched. Osprey B flew at osprey A again and displaced it from the pole.
Osprey A then flew inland, away from the nest area. Osprey A returned at 1459 H to perch again at the side of the
railroad bed, but left the area within 2 min. It still had the alewife in its talons when it left.

By 1502 H the female on the nest had stopped calling and osprey B was the only male that remained in the area.

March 1996

Letters

Because the female had stopped calling while osprey B was still in view, it is likely that osprey B was her mate; the
female generally called in the presence of intruders and never called when only her mate was present. In addition,
osprey B behaved aggressively toward all of the males entering the nest area. Osprey B left the nest area without
returning to the nest, however, so the identification of osprey B is not certain.

The use of a rock as a tool by an osprey has not previously been reported. Rock-dropping behavior has been reported
in Egyptian vultures {Neophron percnopterus), which drop rocks on ostrich {Struthio cameius) eggs to open them (J.
Alcock 1970, Ibis 112:542). Rock dropping has also been reported by Janes (1976, Condor 78:409), who observed
nesting common ravens {Corvus corax) dropping rocks on human intruders. Hypotheses explaining the osprey’s rock-
dropping behavior include the following: (1) if osprey B was the breeding male at the Wilcox West nest, it may have
used the rock to displace an intruding male from the nest area, or (2) the rock-dropping behavior may have been
displacement activity, irrelevant behavior produced by the interplay of conflicting drives (T.L. Gould 1982, Ethology,
Norton, New York, NY U.S.A.).

Some birds have been observed to demonstrate considerable intelligence (e.g., T.H. Turney 1982, Bull. Psychon. Soc.
19:59-62; I.M. Pepperberg 1983, Anim. Learn. Behav. 11:179-185); the observed incident of rock-dropping by an
osprey suggests the possibility that ospreys are capable of insight learning (see J.C. Welty and L. Baptista 1988, The
life of birds, Saunders, New York, NY U.S.A.). Osprey B may have redirected a nest-material-carrying mechanism
to solve a new problem: that of an agonistic encounter with osprey A. Heinrich (1988, Condor 90:271-274) suggested
that the rock-dropping behavior observed in ravens by Janes may have been purposeless displacement activity. This
hypothesis could also explain the rock-dropping behavior of osprey B. — John P. Roche, Department of Biological
Sciences, Central Connecticut State University, New Britain, CT U.S.A, Present address: Center for the Integrative
Study of Animal Behavior, Indiana University, 402 N. Park Ave., Bloomington, IN 47405 U.S.A.

Winter Carrion Feeding of
Red-tailed Hawks in Oklahoma

The red-tailed hawk {Buteo jamaicensis) is one of the best-known, most widely distributed hawks in North America
(P.A. Johnsgard 1990, Hawks, eagles, and falcons of North America. Smithsonian Inst. Press, Washington, DC U.S.A.;
C.R. Preston and R.D. Beane 1993, Red-tailed hawk. Pages 1-24 in The birds of North America, No. 52. Acad. Nat.
Sci., Philadelphia, PA U.S.A.). Studies of red-tailed hawk diets revealed that the prey was mainly small mammals,
but also birds, reptiles, amphibians, and insects (S.K. Sherrod 1978, Raptor Res. 12:49-121; Johnsgard 1990; Preston
and Beane 1993). Red-tailed hawks usually hunt live prey; incidents of carrion feeding in this species are few and
scattered (Sherrod 1978). However, carrion feeding is difficult to document using traditional pellet and stomach content
analyses (P.L. Errington 1933, Condor 35:19-29; P.L. Errington and W.J. Breckenridge 1938, Wilson Bull. 50:113-
121; Preston and Beane 1993). Here we report three observed incidences of carrion feeding by adult red-tailed hawks
in northcentral Oklahoma during late winter 1993.

On 26 February 1993, at about 1000 H, an adult red-tailed hawk was observed feeding on the decaying carcasses
of fish in the backyard of a home in Meeker, Oklahoma. Several domestic cats {Felis domesticus) were feeding on the
fish when the hawk chased them away. The hawk then fed on the fish for almost 1 5 min, and it returned several hours
later on the same day to continue feeding on the fish. On 1 March 1993, at about 1645 H, an adult red-tailed hawk
was seen perched on a freshly killed domestic cat in the middle of a small, two-lane paved road in Stillwater, Oklahoma.
The hawk was observed to feed on the cat for about 20 min. On 2 March 1993, at about 1330 H, an adult red-tailed
hawk was seen sitting on the carcass of an adult eastern cottontail {Sylvilagus floridanus) along the shoulder of a two-
lane highway approximately 6.5 km west of Stillwater, Oklahoma. The hawk was observed to feed on the rabbit for
about 15 min, interrupted only by passing cars.

Small amounts (<2% of diet) of mammalian and avian carrion were found in red-tailed hawk winter diets in Iowa,
Wisconsin, Minnesota, South Dakota, and California (Errington 1933, Condor 35:19-29; Errington and Breckenridge
1938, Wilson Bull. 50:113-121; Fitch et al. 1946, Condor 48:205-234). Carrion made up only 1.2% of the red-tailed
hawk diet from across the U.S. with all 13 cases of suspected carrion feeding occurring between mid-November and

Letters

VoL. 30, No. 1

late February (A.K. Fisher 1893, USDA Div. Ornithol. Mammal., Bull. 3, Washington, DC U.S.A.). Carrion feeding
by red-tailed hawks may be more prevalent than food habit studies suggest, particularly in winter in locations where
favored prey become scarce. However, it remains unclear when carrion becomes acceptable as food to red-tailed hawks.
Red-tailed hawks in Arkansas concentrated winter feeding activities around poultry farms where carrion (dead chickens)
was readily taken (D. James pers. comm.). However, fresh carcasses located near nests were never used by Alaskan
red-tailed hawks, even during food shortages (C.M. Lowe 1978, M.S. thesis, Univ. Alaska, Fairbanks, AK U.S.A.).
Red-tailed hawks apparently have a remarkable capacity for modifying their diet to accommodate local prey including
carrion. In addition to stomach and pellet content analyses, field observations of feeding red-tailed hawks can shed
some light on the types of food red-tailed hawks or other raptor species will take when prey are scarce.

We thank Jim Lish, Charles Preston, and Karen Steenhof for helpful suggestions on an earlier draft of this manuscript
and John Couch, Doug James, Marcus Koenen, John Shackford, and Don Wolfe for discussions on red-tailed hawk
food habits.— Steven R. Sheffield and Noble Jobe, Department of Zoology, Oklahoma State University, Stillwater,
OK 74078 U.S.A. Present address of Sheffield: Department of Environmental Toxicology, Clemson University, P.O.
Box 709, Pendleton, SC 29670.

J. Raptor Res. 30(1):44

Fruit-eating Behavior of a Barred
Forest-falcon

Barred forest-falcons (Micrastur ruficollis) are known to prey on reptiles, birds, amphibians, small rodents, and insects
(L. Brown and D. Amadon 1989, Eaglfes, hawks, and falcons of the world. Wellfleet Press, Seacaucus, NJ U.S.A.;
R.K. Thorstrom et al. 1991, Condor 92:237-239; R.K. Thorstrom 1993, M.S. thesis, Boise State Univ., Boise, ID
U.S.A.). I am unaware of any published record of this species feeding on fruits. Here, I describe two observations of
fruit eating by an incubating female barred forest-falcon in Guatemala.

While studying a population of barred forest-falcons in Tikal National Park, Guatemala (17°13'N, 89°36'W), I
observed the same female on 24 April 1989 and 14 April 1991 after she left her nest cavity. On both occasions, after
preening for 2 min, the falcon flew to the ground and immediately began feeding on the small fallen fruits of a palo
de tzol tree (Tikaiia (Blomia) prisca). The bird fed for approximately 1 min during each observation. After it finished
feeding it flew to a perch near the nest, rested briefly, then flew back into the nest cavity. This fruit-eating behavior
occurred at 1-2 wk after egg laying.

Among Falconiformes, frugivory has been documented in swallow-tailed kites (Elanoides forficatus; W.H. Buskirk
and M. Lechner 1978, Auk 95:767-768; T.O. Lemke 1979, Condor 81:207-208.), and in a number of diurnal scavenging
species including the genera Milvus, Gypohierax, Phalcoboenus, Polyborus, Daptrius, and Milvago (L. Brown and D.
Amadon. 1989. Eagles, hawks, and falcons of the world. Wellfleet Press, Seacaucus, NJ U.S.A.). Frugivory may be
more common in tropical forest raptors than the few reports indicate, but because of dense forest structure and the
secretive behavior of most species, it is difficult to observe.

Acknowledgments

These observations were collected as a part of the Maya Project, a multi-year research effort being conducted in
Guatemala by The Peregrine Fund, Inc. in cooperation with the Instituto Nacional de Antropologia y Historia
(IDAEH), Centro de Estudios Conservacionistas (GECON), Guatemala, and Consejo National de Areas Protegidas
(CONAP), Guatemala. I thank Rogel Chi Ochaeta, Acting Administrator, and the other staff of Tikal National Park,
Guatemala. I owe a special thanks to William Burnham, David Whitacre, J. Peter Jenny, and Lloyd Kiff of The
Peregrine Fund, Inc. for their support, suggestions and assistance. — Russell Thorstrom, The Peregrine Fund, Inc.,
5666 West Flying Hawk Lane, Boise, ID 83709 U.S.A.

J Raptor Res. 30(1 );45

A Preen Gland Abnormality in a Free-living
White-headed Vulture {Aegypius occipitalis)

The uropygial (preen) gland produces oil which enhances the integrity and waterproofing of a bird’s plumage. In
African Old World vultures, preening, coupled with sunning behavior, plays a part in feather maintenance (D.C.
Houston, 1980, Ibis 122:366-369). Although examination of the uropygial gland has long been reeommended as a
routine part of clinical examination of raptors (J.E. Cooper, 1985, Veterinary aspects of captive birds of prey. Standfast
Press, Gloucester, U.K.), little has been published on preen gland abnormalities in these birds, especially in the wild.

Here pathological findings in the preen gland of a white-headed vulture {Aegypius occipitalis) from Tanzania, East
Africa, are reported. The vulture, an adult, was found dead under a tree in Mikumi National Park. No signs of
predation or other injury that might have caused its death were noted. The carcass, which appeared to be fresh, had
been briefly placed in a freezer at the park. Gross postmortem examination revealed that the bird was a female in
good condition (mass 4.5 kg) with substantial subcutaneous fat. Radiographs showed no skeletal changes suggestive of
trauma, nutritional/metabolic disorders, or infectious disease. The only external abnormalities noted were damage to
the tips of wing and tail feathers and a turgid preen gland from which dirty white toothpaste-like material rather than
oil could be expressed.

Histopathological examination of the preen gland revealed some dilated acini and ducts lined by simple, squamous
epithelium; elsewhere, the gland showed whorls of keratin, stratified squamous and giant cells in close proximity to
secretory material. In a seeond seetion there was moderate hyperkeratinization of the epithelium overlying the gland.

On the basis of these findings the abnormality was diagnosed as a preen gland impaction of uncertain etiology.
Microbiologieal culture was not performed but the histopathological findings, in particular the absence of any heterophil
infiltrate, would appear to rule out a bacterial infection. The stratified epithelium suggests a metaplastic change in
the gland and the giant cells may have been a response to keratin.

The uropygial gland abnormality in this vulture did not appear to have contributed to death nor was it associated
with any obvious changes in the bird’s plumage. The cause of the impaction was unclear as has been the case in preen
gland impactions reported in other species of bird including budgerigars {Melopsittacus undulatus; M.L. Petrak, 1982,
Diseases of cage and aviary birds. Lea and Febiger, Philadelphia, PA U.S.A.), helmeted guineafowl {Numida meleagris;
Cooper unpubl. data), and merlins {Falco columbarius] J.E. Cooper and N.A. Forbes, 1986, Vet. Rec. 118:232-235).
The only other impaction of this kind diagnosed in an East African raptor by the author involved a live tawny eagle
{Aquila rapax) which was found trapped, with heavily soiled plumage, on the edge of a soda lake in Kenya (Cooper
unpubl. data). The underlying pathogenesis was not elucidated.

I am grateful to the staff of Mikumi National Park and ABRU, especially Sabine Schmidt, Christopher Holmes
and JoAnn Dokter, for providing the specimen, and to colleagues at the Faculty of Veterinary Medicine for taking
radiographs and preparing histological sections. — John E. Cooper, Faculty of Veterinary Medicine, Sokoine Uni-
versity of Agriculture, P.O. Box 3021, Morogoro, Tanzania. Present address: Durrell Institute of Conservation and
Ecology, The University, Canterbury, Kent CT2 7PD U.K.

Commentary

On Winter Records and Vertebrate Prey in
Flammulated Owls

Denver W. Holt

Owl Research Institute, P.O. Box 8335, Missoula, MT 59807 U.S.A.

Recent literature has questioned the authenticity of late
season sight records and vertebrate prey in flammulated
owls {Otus fiammeolus; McCallum 1994a, b). Herein, I
revisit an earlier report (Holt et al. 1987), which has been
questioned by McCallum (1994a, b). Additionally, I re-
view and try to clarify other reports of late season sight
records and vertebrate prey from flammulated owls that
I believe were misinterpreted by McCallum (1994a, b).

Data Revisited

Holt et al. (1987) reported the following seemingly un-
usual fall and winter flammulated owl records: (1) In
January 1965, a flammulated owl was found helpless in
snowstorm and later died; (2) On 21 November 1981, a
flammulated owl was observed perched in a tree with a
vole in its talons; and (3) On 20 December 1981, a flam-
mulated owl was observed chasing passerines at a bird
feeder. These records were scrutinized by me and Philip
L. Wright, and all persons making the observations were
interviewed. Two of the records in 1981 came from bi-
ologists, and the 1965 record was from a birder. The
biologist who submitted the report of the owl with a vole
is an experienced birder and is familiar with Montana
owls. She and her husband observed the owl from a dis-
tance of about 8 m for 1 min. A report of a flammulated
owl chasing passerines at a feeder was confirmed second
hand by a raptor biologist who knew the observer. This
observer died before we could speak to him. The person
who picked up the flammulated owl in the blizzard kept
it in a cage and had an experienced birder confirm its
identity using bird field guides. The owl died 1 d later
and was discarded.

McCallum (1994a) stated that “If seen, the flammu-
lated owl is easily identified by the unique combination
of small size and dark eyes,” but then goes on to say that
November and December records of flammulated owls in
Montana (one with prey, and one chasing passerines at a
feeder) are misidentifications. Again, McCallum (1994a)
stated that “An unpreserved specimen and two sight re-
cords in Montana (Holt et al. 1987) are poorly documented
and dubious.” Yet he also stated that in “North America,
it occurs in lowlands peripheral to breeding habitat in
October, sparingly in November, and occasionally in De-

cember” (but see Linkhart and Reynolds 1987). Once
again, McCallum (1994a) referring to the Montana re-
cords and one Christmas bird count record from Wash-
ington, stated that “each of these records is individually
unlikely. ...” He then continues to state that the geo-
graphic concentration of these reports carries some weight.
The flammulated owl breeds in Montana, and is now
known to be much more common than previously believed.

McCallum continues with: “The assertion that small
vertebrates are taken has been reported for a century with-
out convincing documentation.” But, he then cited con-
clusive and convincing data: “Smith (1891) took a female
whose stomach contained the remains of some small ro-
dents.” Bull and Anderson (1978) found a pellet contain-
ing the remains of a red-backed vole {Clethrionomys gap-
peri) below an active flammulated owl nest tree and dark-
eyed junco (Junco hyemalis) feathers in another active nest.
This was restated in McCallum (1994b) as “the previous
occupants (e.g., northern saw-whet owl [Aegolius acadicus],
may have taken these prey (E. Bull fide. Cannings pers.
comm.).” But Bull (pers. comm.) did not know if northern
saw-whet owls or any other species nested in this same
cavity the same year prior to the flammulated owls, or in
previous years. Linkhart and Reynolds (1994) found a
15-20 g deer mouse (Peromyscus sp.) carcass in a flam-
mulated owl nest. The carcass smelled of decay and lid
had lapsed between visits by the researchers. Although a
1-cm^ spot of pelage on the mid-dorsal area was missing,
no obvious punctures or talon marks were observed. The
authors were not able to skin the carcass and examine it
for subcutaneous hemorrhages, as an indication of pre-
dation (see Holt 1994). Linkhart and Reynolds (1994)
offered three alternate explanations, aside from the mouse
having been killed by the owl, as to how the carcass got
there. They concluded that direct evidence of flammulated
owls capturing vertebrates is still lacking. But McCallum
(1994a) incorrectly paraphrased their results, and stated
that Linkhart and Reynolds (1994) said “another species
was responsible for killing it.” Linkhart and Reynolds
(1994) said no such thing. Although one of their alternate
explanations was that a northern saw-whet owl or north-
ern pygmy-owl {Glaucidium gnoma) could have brought
the deer mouse to the nest in response to food begging calls
of the young flammulated owls. It is not unusual for owls
to leave uneaten prey in the nest both during breeding and

March 1996

Commentary

after dispersal from the nest — particularly cavity nesters
(D. Holt pers. obs.).

Cannings (1994) received a dead flammulated ow^l on
1 5 November 1 988, from southern British Columbia, Can-
ada, which contained the remains of a dusky shrew (Sorex
monticolus). Cannings concluded that it was the first def-
inite record of flammulated owls eating vertebrate prey
(but see Smith 1891). Finally, McCallum (1994a) himself
reported the legs of a juvenile mountain chickadee {Parus
gambeli) in a flammulated owl nest. He concluded “that
some flammulated owls over-winter in northern areas by
subsisting on vertebrates cannot be completely discount-
ed,” In Colorado, mean body mass of breeding female and
male flammulated owls was 65.6 g (SD = 10.85, N = 25)
and 54.7 g (SD = 3.28, N = 27), respectively (Reynolds
and Linkhart 1987). Mean body mass of the similar-sized
northern pygmy-owl females is 73.0 g (N =10) and males
61 .9 g {N = 42) (Earhart and Johnson 1970). Yet northern
pygmy-owls kill and consume a wide range of vertebrates
from shrews (Sorex spp., 3 g) to flickers (Colaptes spp.,
167 g), with mean mass about 38 g for both avian and
mammalian prey (Holt and Leroux 1996). It has been
said that flammulated owls have “weak” feet (McCallum
1994b), and this has been assumed to be one reason why
they cannot kill vertebrate prey. I know of no quantitative
data to support or refute this statement. However, rap-
torial feet are used for seizing prey (although lethal wounds
cannot be ruled out) and it is often the bill that delivers
the killing bite to the occipital region of the skull or by
snapping the cervical vertebrate.

New Data

K. McKeever (pers. comm.) reported that when offered
a choice of insects or dead lab mice (Mus musculus) weigh-
ing 12-20 g, a captive-breeding female flammulated owl
almost always took the mice. Similarly the male, almost
always took 12-15 g mice back to the nestlings. And both
always took the larger mice over smaller ones. McKeever
has also observed that 20 g mice were difficult for the owls
to eat, but 12-15 g mice were effectively consumed. This
is not proof of killing, but certainly the willingness and
ability to consume mice. Carl Marti (pers. comm.) found
two dried juvenile Peromyscus carcasses in a flammulated
owl nest after the young owls had fledged. No evidence of
the mice nesting in the box was evident, and they were
not there prior to flammulated owl nesting. Cause of death
could not be determined.

In October 1994, the Montana Verification Record
Committee accepted another fall record for a flammulated
owl — 10 November 1993. And, on 19 November 1994, a
flammulated owl was observed and very well described by
a hunter in western Montana. This record is currently
under review.

Why have researchers been so cautious in accepting that
flammulated owls may occasionally eat vertebrate prey
and occur during fall and winter particularly in the north-
ern part of the species’ range where we know very little
about their natural history? Noctuid moths — a primary
food item in Colorado (Reynolds and Linkhart 1987) —
are commonly found throughout November in Montana
(D Holt pers. obs.). Furthermore, in Colorado, postnest-
ing adult flammulated owls remain on their breeding

grounds (about 2400-3000 m elevation) to about 12 Oc-
tober (Linkhart and Reynolds 1987). R. Reynolds (pers.
comm.) stated that flammulated owls are able to withstand
very cold spring nights, provided food is available. Dietary
analysis of flammulated owls has been conducted primarily
from May through October in Colorado (R. Reynolds
pers. comm.), but see McCallum (1994a, b) for other
studies. No studies have yet addressed the diet of flam-
mulated owls in the northern limits of their range. Al-
though captive situations and laboratory experiments may
be helpful in determining if flammulated owls can capture,
kill and consume various-sized vertebrate prey, caution
should be taken in extrapolating from these results.

In retrospect. Holt et al. (1987) could have provided
more data, even direct quotes concerning these records.
McCallum’s concerns likely stemmed from the vertebrate
prey reported, and the lack of specimens and photographs.
I believe scientists should be judicious, but I also feel that
we cannot only believe ourselves — ^there are many qual-
ified people in the field.

Acknowledgments

I thank Richard Reynolds, Philip L. Wright, Richard
Cannings and Archibald McCallum for comments on this
manuscript.

Literature Cited

Bull, E.L. and R.G. Anderson. 1978. Notes on flam-
mulated owls in northeastern Oregon. Murrelet 59:26-
28.

Cannings, R. J. 1 994. A flammulated owl eats vertebrate
prey in late fall. Northwest Nat. 75:30-31.

Earhart, C.M. and N.K. Johnson. 1970. Size di-
morphism and food habits of North American owls.
Condor 72:251-264.

Holt, D.W. 1994. Effects of short-eared owls on com-
mon tern colony desertion, reproduction, and mortality.
Colon. Waterbirds 17:1-6.

AND L.A. Leroux. 1996. Diets of northern pyg-

my-owls and northern saw-whet owls in west-central
Montana. Wilson Bull. In press.

, J.A. Hoy AND P.L. Wright. 1987. Occurrence

and first nest record of flammulated owls in Montana.
J. Raptor Res. 21:120-121.

Linkhart, B.D. and R.T. Reynolds. 1987. Brood di-
vision and postnesting behavior of flammulated owls.
Wilson Bull. 99:240-243.

AND . 1994. Peromyscus carcass in the

nest of a flammulated owl. /. Raptor Res. 28:43-44.
McCallum, D. A. 1994a. Flammulated owls. Pages 14-
46 in G.D. Hayward and J. Verner [Eds.], Flam-
mulated, boreal, and great gray owls in the United
States: a technical conservation assessment. USDA For.
Serv. Gen. Tech. Rep. RM-253, Fort Collins, CO
U.S.A.

. 1994b. Flammulated owl. In A. Poole and F.

Gill [Eds.], The birds of North America, No. 93, Acad.

Commentary

VoL. 30, No. 1

Nat. Sci., Philadelphia, PA and Am. Ornithologists’
Union, Washington, DC U.S.A.

Reynolds, R.T. and B.D. Linkhart. 1987. The nest-
ing biology of flammulated owls in Colorado. Pages
239-248 in R.W. Nero, R.J. Clark, R.J. Knapton and

R.H. Hamre [Eds.], Biology and conservation of north-
ern forest owls. USDA For. Serv. Gen. Tech. Rep.
RM-142, Fort Collins, CO U.S.A.

Smith, W.G. 1891. Nesting of the flammulated screech
owl. Ornithol. and Oolog. 16:27.

Diurnal Sight Records of Flammulated Owls
AND Possible Vertebrate Prey in Winter:

THE Case for Caution

D. Archibald McCallum

Department of Biology, College of Charleston, Charleston, SC 29424, U.S.A.

Holt (1996) questions my questioning (McCallum
1994a, b) of three Montana sight records of the fiam-
mulated owl {Otus flammeolus) published by Holt et al.
(1987). He goes on to promote the plausibility of those
records by revisiting two poorly understood facets of flam-
mulated owl biology: winter range and facultative carniv-
ory. Further discussion of these unusual records, and of
flammulated owl biology, is entirely salutary, particularly
if it leads to more research on these questions. My main
concern in retaining my cautious stance with regard to
diurnal sight records in winter in Montana, as well as
more general inferences of active carnivory, is that we do
not falsely attribute to this owl a level of ecological flex-
ibility that it does not possess.

Four regions of the USDA Forest Service classified this
forest owl as sensitive (Verner 1994), independently of my
review of the literature (McCallum 1994b) and conser-
vation assessment (McCallum 1994c) of the species. Al-
though this species appears to be common in some pon-
derosa pine (Pinus ponderosa) and semiarid montane mixed
conifer stands throughout the western U.S. and southern-
most British Columbia, I found three major reasons to be
concerned for the future of the flammulated owl: (1) All
known clutches contained 2-4 eggs, and hence this species
appears to lack the capacity, possessed by some other owls
(e.g , snowy owls [Nyctea scandiaca], Parmelee 1992 and
barn owls [Tyto alba], Marti 1992), to produce large clutches
when food is superabundant. Coupled with a possible
preference for older forests (Reynolds and Linkhart 1992),
this demographic inflexibility suggests a species that may
not recover quickly from disturbance or habitat alteration.
Indeed, Marshall (1988) found only two territories in 1986
in a logged area that had supported 18-20 territories in
1938 (Marshall 1939). (2) Almost all independently ver-
ifiable evidence indicates that the flammulated owl subsists
entirely on arthropods in the wild. Broad spectrum insec-
ticides used in intensive forest management may have a
negative impact on reproductive success if they severely
reduce the abundance or diversity of the owl’s prey base.
(3) Winter (1974) concluded, after a thorough review of
available evidence, that the species is a trans-latitudinal
migrant. Following a review of evidence obtained more
recently, I concurred with Winter’s conclusion. If it is true
that the flammulated owl is a trans-latitudinal migrant,
and further that the bulk of the population winters no
further north than central Mexico, as the very limited

evidence presently available suggests (McCallum unpubl.
data), then the fate of the species may hinge on habitat
quality outside the United States.

The sight records under discussion (Holt et al. 1987,
Holt 1996) are inconsistent with items 2 (lack of verte-
brates in diet) and possibly 3 (migratory behavior) above
This inconsistency does not mean that they were errone-
ous. It does suggest that the data presented in support of
such records should be beyond question. While I would
like very much to believe these records, because their truth
would imply that the flammulated owl is much more flex-
ible ecologically than I fear, I do not think the supporting
data are beyond question.

What we need for records that extend the verified north-
ern margin of the winter range of the species from the
deserts of Arizona and California (American Ornitholo-
gists’ Union 1983) as far north as Montana is not second-
hand sight records, regardless of the qualifications and
experience of the observers, but photographs, recordings,
and specimens. Only data that can be independently ver-
ified should be allowed to change the range of the species
so drastically. The same argument holds for diet. Such
caution is dictated by both the conservation implications
of these records, and by standard scientific practice. Items
2 and 3 above constitute null hypotheses against which
the Montana records must be tested. I cannot reject those
null hypotheses with anything approaching 957o confi-
dence.

The January 1965 record is the most believable of the
three, because it involved extended observation of a bird
in captivity by an experienced birder with field guides in
hand. Indeed, grounded flammulated owls are often picked
up after snowstorms (e.g., Ligon 1968, Webb 1982). The
major doubt about this record is its date, because memory
can become inaccurate over long periods of time. Holt
(pers. comm.) informs me that the person who found it
remembered the date unhesitatingly as January, when
interviewed in the 1980s. In fact, my only negative com-
ment about this record was that it was “dubious” as com-
pared to several specimen records. One can hardly disagree
with such a comparison.

The dates of the two 1981 records are not overly prob-
lematical, as November sight records have been accumu-
lating from throughout the U.S. breeding range of the
species in recent years (McCallum unpubl. data). It is the
implication of active hunting of vertebrates that is prob-

Commentary

VoL. 30, No. 1

lematical. In his commentary, Holt (1996) reviews records
of vertebrate remains associated with flammulated owls,
particularly in their nests. It is clear that captive birds will
readily consume vertebrate remains, but I have made this
point clearly myself (McCallum 1994a, b). In two cases,
vertebrate remains have been found in flammulated owl
stomachs (McCallum 1994a, b, Holt 1996). In several
cases vertebrate remains were found in or below active
nests. In none of these cases, however, was a flammulated
owl seen to capture or even attack a vertebrate, including
the new data supplied by McKeever (Holt 1996). Even the
shrew found in the stomach of a British Columbia bird in
November (Cannings 1994) could have been found dead
while the owl was foraging in the leaf litter for earwigs,
which also were present in the stomach.

The 20 December 1981 record is the only report of
active hunting of vertebrates known to me. Perhaps this
bird was not hunting, but instead had been flushed by
mobbing passerines. F.R. Gehlbach and I witnessed mob-
bing of a flammulated owl that we flushed from a nest in
New Mexico. Without more details, one cannot be con-
fident that the owl in this case was attempting to capture
another bird. This and the other 1981 record are the only
reports known to me of foraging in full daylight by this
completely nocturnal species. Although time of day was
not mentioned in the published account (Holt et al. 1987),
Holt has confirmed (D.R. Holt, pers. comm.) that both
were diurnal. Given the uniqueness of these records if they
are true, I would expect more confirmatory details, on
such features as iris color, overall shape, flight character-
istics, number of times passerines were “chased,” etc.

In his commentary, Holt (1996) has scrutinized my
writings for inconsistencies, rather than providing con-
firmatory details. Inconsistencies in my review of the topics
of the killing and eating of vertebrate prey (McCallum
1 994a, b) stem from the inconsistency of the evidence. The
evidence for these behaviors is both scanty and entirely
circumstantial (in the case of killing). Yet, I chose not to
censor these anecdotes. Indeed, I went as far as repeating
some very dubious statements by Karalus and Eckert
(1974), in the interest of completeness. Having reported
all the data I could find that supported carnivory, I was
unconvinced by the strictly circumstantial evidence they
provided. Holt’s (1996) implied argument that flam-
mulated owls should be able to kill vertebrates because
similar-sized northern pygmy-owls {Glaucidium gnoma) do
so is even less convincing. I consider extrapolating from
Glaucidium to Otus extremely risky. Even the larger Otus
species are mainly insect eaters according to Marshall
(1967), so the size similarity between northern pygmy-
owls and flammulated owls is not so relevant as their
phylogenetic difTerences.

In summary, I must say that I remain less than totally
convinced that the birds seen clutchinq a vole and “chasing
passerines” during broad daylight were flammulated owls.
Although I tend to believe the account of the bird found

in a blizzard, my personal opinion is that it is insufficiently
documented to become part of the record of the range of
this species. McKeever’s observation that a pair of captive,
breeding flammulated owls prefer large dead mice to in-
sects (Holt 1996) supports the idea that carcasses of ver-
tebrates found in flammulated owl nests in the wild may
have been taken there by adults of this species. Ironically,
such an interpretation argues against active hunting and/
or killing. If dead vertebrates (e.g., mice) are preferred,
the most plausible reason they so seldom appear in the
diets of adults and nestlings (McCallum 1994a, b) is that
live vertebrates are uneconomical or impossible to obtain.
Clearly, an experimental study of both prey preference
and the ability to capture and kill vertebrates would be
highly desirable. Indeed, I hope that the major outcome
of the present discussion will be increased efTorts by or-
nithologists and birders to learn whether flammulated owls
can and do kill vertebrates, and whether they winter reg-
ularly anywhere inside the United States.

Literature Cited

American Ornithologists’ Union. 1983. Check-list
of North American birds, 6th ed. Washington, DC
U.S.A.

Cannings, R. J. 1 994. A flammulated owl eats vertebrate
prey in late fall. Northwest Nat. 75:30-31.

Holt, D.W. 1996. On winter records and vertebrate
prey in flammulated owls. /. Raptor Res. 30:46-48.

, J.A. Hoy and P.L. Wright. 1987. Occurrence

and first nest record of flammulated owls in Montana.
/. Raptor Res. 21:120-121.

Karalus, K.E. and A.W. Eckert. 1974. Flammulated
owl. Pages 156-162 in The owls of North America
(north of Mexico). Doubleday and Co., Garden City,
NY U.S.A.

Ligon, J.D. 1968. Starvation of spring migrants in the
Chiricahua Mountains, Arizona. Condor 70:387-388.
Marshall, J.T. 1939. Territorial behavior of the flam-
mulated screech owl. Condor 41:71-78.

. 1967. Parallel variation in North and Middle

American screech-owls. Monogr. West. Found. Vert Zool.
1:1-72.

. 1988. Birds lost from a giant sequoia forest

during fifty years. Condor 90:359-372.

Marti, C.D. 1992. Barn Owl. In A Poole, P. Stetten-
heim, and F. Gill [Eds.], The birds of North America,
No. 1, Acad. Nat. Sci., Philadelphia, PA and Am.
Ornithologists’ Union, Washington, DC U.S.A.
McCallum, D,A. 1994a. Flammulated owl. In A. Poole
and F. Gill [Eds.], The birds of North America, No
93, Acad. Nat. Sci., Philadelphia, PA and Am. Or-
nithologists’ Union, Washington, DC U.S.A.

. 1994b. Review of technical knowledge: flam-
mulated owls. Pages 14-46 in G.D. Hayward and J
Verner [Tech. Eds.], Flammulated, boreal, and great

March 1996

Commentary

gray owls in the United States: a technical conservation
assessment. USDA For. Serv. Gen. Tech. Rep. RM-
253, Ft. Collins, CO U.S.A.

1994c. Conservation status of flammulated owls

in the United States. Pages 74-79 in G.D. Hayward
and J. Verner [Tech. Eds.), Flammulated, boreal, and
great gray owls in the United States: a technical con-
servation assessment. USDA For. Serv. Gen. Tech.
Rep RM-253, Ft. Collins, CO U.S.A.

Parmelee, D.F. 1992. Snowy Owl. In A. Poole, P.
Stettenheim, and F. Gill [Eds.], The birds of North
America, No. 10, Acad. Nat. Sci., Philadelphia, PA
and Am. Ornithologists’ Union, Washington, DC
U.S.A.

Reynolds, R.T., and B.D. Linkhart. 1992. Flam-
mulated owls in ponderosa pine: evidence of preference

for old growth. Pages 166-169 in Old-growth forests
in the Southwest and Rocky Mountain Regions: pro-
ceedings of a workshop. USDA For. Serv. Gen. Tech.
Rep. RM-213, Ft. Collins, CO U.S.A.

Verner, J. 1994. Current management situation: flam-
mulated owls. Pages 10-13 in G.D. Hayward and J.
Verner [Tech. Eds.], Flammulated, boreal, and great
gray owls in the States: a technical conservation as-
sessment. USDA For. Serv. Gen. Tech. Rep. RM-253,
Ft. Collins, CO U.S.A.

Webb, B. 1982. Distribution and nesting requirements
of montane forest owls in Colorado. Part III: flam-
mulated owl {Otus flammeolus). /. Colo. Field Ornithol.
16:76-81.

Winter, J. 1974. The distribution of the flammulated
owl in California. West. Birds 5:25-44.

BOOK REVIEWS

Edited by Jeffrey S. Marks

J. Raptor Res. 30(1):52

Raptor Migration Watch-Site Manual: A Co-
operative Strategy for Protecting the World^s Mi-
gratory Raptors. Edited by Keith L. Bildstein and
Jorje I. Zalles. 1995. Hawk Mountain Sanctuary
Association, Kempton, PA. vi + 177 pp. Paper,
$20.00. English and Spanish versions available from:
Hawks Aloft Worldwide, Hawk Mountain Sanc-
tuary, R.R. 2, Box 191, Kempton, PA 19529. —
Pennsylvania’s Hawk Mountain Sanctuary has been
a leader in the conservation of migratory raptors for
more than 60 yr. Recognizing that the need for pro-
tection transcends international boundaries, in 1988
the Sanctuary established a cooperative global con-
servation initiative called Hawks Aloft Worldwide.
Two important goals of the project are the identi-
fication of raptor migration sites throughout the world
and the training of local conservationists to oversee
activities at these sites. Toward achieving these goals,
the Sanctuary prepared this manual as a guide to
operators of hawk-watching sites.

The manual contains 13 chapters, each with a
thorough list of references. The introductory chapter
provides a brief history of Hawk Mountain Sanc-
tuary, identifies general threats to migrating raptors,
and discusses the Sanctuary’s upcoming World Atlas
of Raptor Migration Watch-Sites. Chapters 2-5 are
devoted to biological issues. “Raptor Migration and
Conservation Biology” (Chapter 2) gives a general
overview of taxonomy, classification, migration be-
havior, and legal protection, and includes a list of
globally threatened raptors. “Investigating Raptor
Migration Biology and Ecology” (Chapter 3) pro-
vides an annotated list of scientific topics suitable for
investigation at migration watch-sites. Chapter 4
(“Monitoring the Abundance and Distribution of
Migrating Raptors”) discusses methodology, includ-
ing identification, counting techniques, and moni-
toring population trends. Chapter 5 (“Managing
Data”) provides a useful introduction to data man-
agement techniques.

Chapters 6-10 consider the human aspects, in-

cluding environmental education, ecotourism, and
membership and volunteer programs. The “Watch-
Site Diagnostic” (Chapter 1 1) is a tool for generating
“a detailed description of the physical setting, insti-
tutional framework, resource base, and overall sit-
uation of a watch-site.” The closing chapters contain
a comprehensive bibliography of papers on raptor
migration in Latin America (Chapter 12) and ab-
stracts from seven Latin American projects that were
discussed at the recent Hawks Aloft Worldwide
workshop held in Veracruz, Mexico (Chapter 13).

Clearly, much care and thought went into pro-
ducing this manual. It provides an abundance of
information that will be of interest to raptor enthu-
siasts in general, and it will be virtually indispen-
sable to anyone who is contemplating operating a
migration watch-site. — Jeff Marks, Cooperative
Wildlife Research Unit, University of Montana,
Missoula, MT 59812 U.S.A.

The Northern Goshawk: Ecology and Man-
agement. Edited by William M. Block, Michael L.
Morrison, and M. Hildegard Reiser. 1994, Studies
in Avian Biology, No. 16. vi -I- 136 pp., 39 figures,
57 tables, 2 appendices. ISBN 0-935868-76-3. Pa-
per, $16.00. — This collection of papers is the result
of a Cooper Ornithological Society symposium held
in Sacramento in April 1993 and organized by R.T.
Reynolds, D.A. Boyce, Jr., and the above-named
editors. The symposium included 31 oral presen-
tations. After peer review, 22 papers were published
in the proceedings: six under a section entitled “Re-
search Approaches and Management Concepts,” nine
under “Resource Ecology,” and seven under “Pop-
ulation Ecology.” The introduction states: “The cur-
rent situation with the northern goshawk {Accipiter
gentilis), a raptor typically dependent on mature

March 1996

Book Reviews

forests, bears an uncanny resemblance to that of the
northern spotted owl [Strix occidentalis] a decade ago.
Within the past five years, evidence has arisen to
suggest that populations of northern goshawks are
declining, particularly in the western United States
. . . This collection of papers represents the current
state of knowledge on northern goshawks.”

I will start by relating some of the important new
information for a range of topics in the proceedings.
Owing to space limitations, I will not critique in-
dividual papers. I conclude with an evaluation of
the degree to which the proceedings represent “the
current state of knowledge” on goshawk ecology and
management.

Under “Research Approaches,” C. Boal offers an
excellent and much-needed guide to the appearance
and behavior of nestling goshawks at different ages.
S. Joy et al. provide a wealth of data and concepts
for anyone interested in improving effectiveness and
efficiency in surveys of forest hawks.

Under “Resource Ecology,” C. Hargis et al. and
D. Bright-Smith and R. Mannan reported mean
home ranges (95% harmonic mean) of about 15 km^
during summer. Radio locations were generally in
stands that had larger trees with denser canopies
than typical for the study area. Unlike some re-
searchers, Bright-Smith and Mannan recognized that
their birds were not a random sample of the study
population; thus, they compared habitats at radio
locations with habitats available within each bird’s
home range. P. Kennedy et al. present data on move-
ments of young birds in northern New Mexico. They
suggest managing for a postfledging area (PFA) of
about 168 ha. Theory on the ecological basis for
PFAs could be strengthened by a telemetry study
that tracked adults and their young simultaneously.

F. Doyle and J. Smith tracked a goshawk pop-
ulation through a “cycle” of prey availability (mostly
snowshoe hares [Lepus americanus]) in the Yukon.
During both nesting and winter seasons, goshawk
densities fluctuated by an order of magnitude with
the highs and lows of the hare cycle. Fledgling pro-
duction averaged 2.8 per occupied nest during the
apex of prey abundance but dropped to zero after
the numbers of key prey species collapsed.

J. Younk and M. Bechard describe goshawk nest-
ing biology in high-desert aspen (Populus tremu-
loides) groves in northern Nevada. The groves av-
eraged 25 ha and usually contained a creek or spring.
Unusually high proportions of breeding females were
in first- or second-year plumage, perhaps a response

to a recent increase in the availability of ground
squirrels. It will be instructive if these birds can be
monitored throughout the next decline in ground
squirrel numbers.

Under “Population Ecology,” P. Detrich and B.
Woodbridge related that 72% of breeding adults lo-
cated in consecutive years retained their mates from
the previous year. Eventually, 18% of adult females
and 23% of adult males were found nesting 4-13
km from the territories where they were marked. In
northern Arizona, Reynolds et al. found that mean
intraterritory movement between alternate nests in
consecutive years was 266 m (range 100-635 m).
Nests produced an average of 2.3 fledglings when
both parents were in full adult plumage but only
1.1 fledglings when one parent was in subadult
plumage.

As evidenced above, this publication presents many
important research results as well as theories worthy
of testing. However, because the proceedings fail to
present information and theories from the full array
of goshawk researchers and management agencies,
the goal of representing the “current state of knowl-
edge on northern goshawks” is not achieved. One
problem is that only two papers are from outside of
the contiguous western United States. No European
researcher was included, presumably because of the
symposium objective “to assemble researchers and
managers from across the country’’^ (emphasis mine).
Yet, I believe that much could be learned by ex-
amining similarities and differences in goshawk ecol-
ogy between continents.

Although several researchers presented papers that
were not published in the proceedings, other North
American goshawk workers were absent altogether.
For example, Arizona Game and Fish Department
researchers had studied goshawks for years, and their
data (especially on canopy coverage and territory
occupancy) would have been a nice addition to the
proceedings.

Moreover, during the 2 yr preceding the sym-
posium, the Southwestern Region of the U.S. Forest
Service was engaged in acrimonious debate with state
and federal wildlife agencies in Arizona and New
Mexico over alternative hypotheses regarding gos-
hawk ecology and forest management. Both sides
had conducted extensive literature reviews and anal-
yses. Although the views of wildlife agencies were
not presented at the symposium, two papers in the
proceedings (Graham et al. and Bassett et al.) de-
scribed and expanded on the Forest Service strategy

Book Reviews

VoL. 30, No. 1

for goshawk management in the Southwest (viz.,
Reynolds et al. 1992, USDA For. Serv. Gen. Tech.
Rep. RM-217, Fort Collins, CO U.S.A.). Discus-
sion of forest management for goshawks also would
have benefited from participation of scientists who
had published journal articles on the subject, as well
as biologists funded by the timber industry and those
who wrote the petition to list the goshawk as an
endangered species in the Southwest. A broader ar-
ray of opinions would encourage managers and sci-
entists to consider and test alternative hypotheses on
goshawk ecology and forest management.

The primary sponsor of the proceedings was the
U.S. Forest Service. Also, four of the five symposium
organizers were Forest Service employees, and three
were authors of the Forest Service strategy. Addi-
tional views would have been presented if other
agencies and groups had cosponsored the sympo-
sium. I am not suggesting any intentional bias on
the part of the symposium organizers, but apparently
the effort was inadequate to obtain a comprehensive
array of scientific opinion.

In conclusion, the proceedings’ goal to represent
“the current state of knowledge” was not achieved.
The effort would have benefited had the proceedings
included more papers from beyond the western Unit-
ed States (especially Europe) and presented a wider
variety of habitat management opinions. The pro-
ceedings also would have been enhanced by three
overviews of goshawk ecology and management, one
each from western North America, eastern North
America, and Europe. Despite my criticisms. The
Northern Goshawk: Ecology and Management pre-
sents significant new research and theories. Given
its relatively low cost, it should be acquired by ev-
eryone interested in accipiters and made available
at most libraries. — D. Coleman Crocker-Bedford,
243 Wood Road, Ketchikan, AK 99901 U.S.A.

Artificial Nest Structures for Ospreys: A Con-
struction Manual. By Peter J. Ewins. 1994. En-
vironment Canada, 25 St. Clair Avenue East, To-
ronto, ON M4T 1M2, Canada, iv + 41 pp., color

cover, 16 black-and-white photographs, 27 figures.
ISBN 0-662-22791-3. Paper, available free from
above address. — Among falconiforms, the osprey
{Pandion haliaetus) may be the first species to have
benefited from the provisioning of artificial nests. As
early as the nineteenth century, farmers in the north-
eastern U.S. were placing old cartwheels atop poles
to encourage ospreys to nest near their homesteads
in the belief that these birds would drive away other
hawks (Abbott 1911). In recent years, man-made
nest structures have become so important an aspect
of osprey conservation and management that in some
areas, most nests now occur on artificial sites.

With this construction manual, Ewins has pro-
duced the most comprehensive compilation of arti-
ficial nest platform designs available. He draws not
only on published sources, but on some obscure agen-
cy reports and unpublished material. The stated em-
phasis is on designs “best suited to the habitats found
in Canada.” Some comparisons with an earlier work
(Martin et al. 1986) may be appropriate. Ewins
incorporates the designs from the Martin et al. pub-
lication, but includes twice as many different designs.
His “Further Reading” contains 1 4 references, how-
ever, whereas Martin et al. list 49 titles.

A brief introduction is followed by one-page sec-
tions on “Site Selection Considerations” and “Gen-
eral Notes on Construction.” The main portion de-
scribing individual platform designs is divided into
three sections according to the type of supporting
structure. The first covers single poles (seven de-
signs), and the second deals with “Other Structures”
(including tripods, tree platforms, a ring platform,
a metal grid, and methods for reinforcing duck blinds
that currently support osprey nests). All of these
designs are illustrated with detailed drawings and/
or photographs, and for some designs the required
construction materials are listed in a box. The third
section deals with osprey nests on power transmis-
sion towers and utility poles. Also included is a de-
cision chart for assisting utility managers in selecting
an appropriate course of action when ospreys nest
on power transmission structures. Several modifi-
cations are suggested to either allow nests to persist
while eliminating (or greatly reducing) the incidence
of short circuits between live wires, or to prevent
nest construction on poles after nests have been moved
to nearby sites. Two additional platform designs are
shown in this section.

One troubling omission is that no attempt is made
to critically evaluate the efficacy and durability of

March 1996

Book Reviews

the various designs. While such information may not
be available for all structures, the usefulness of the
manual would have been enhanced had more use
been made of the practical experience that already
exists. For example, the metal-grid platform used
by the U.S. Coast Guard on navigational aids in the
St. Mary’s River has proven to be quite inadequate
due to a lack of any means of holding nests in place.
Nests on these platforms remain relatively shallow,
and several have been blown off entirely. In one such
instance, two small chicks perished when their feet
became entangled in the metal grid. Although using
a wider mesh, as Ewins suggests, would help anchor
sticks to the platform, it would also increase chances
of finer material in the center of the nest falling
through and thus exposing eggs or chicks to unnec-
essary risk. All platforms must have some structural
feature designed to keep nesting material in place.

I have found that ospreys nesting on platforms
over water and far from shore tend to build only
shallow nests, especially during the first 1-2 yr a
platform is used. Apparently, availability of suitable
nesting material, and the distance over which it must
be carried, influence the size and quality of the nest.
On the shallow offshore nests, the eggs in the nest
bowl often rest on the bare wood of the platform.
Hatching rates of such eggs are low, possibly owing
to inadequate incubation temperatures. One would
expect that this situation would be at least as severe
on wire-mesh substrates. This problem can be al-
leviated by nailing a piece of carpet (about 30 cm^)
to the center of a solid-base platform. On a metal-
grid platform, a similar-sized piece of fine wire mesh
can be fastened at the platform center.

Our Michigan platforms (Postupalsky and Stack-
pole 1974) were initially equipped with wooden
dowels to hold nests in place. Because the dowels
eventually deteriorated and broke off, they were re-
placed with upright rectangular boards attached to
angle brackets. Similar modifications may become
necessary for other platform types that use wooden
dowels.

In the preceding paragraphs, I have attempted to
evaluate several artificial nest designs, drawing on
my three decades of experience with osprey nesting
platforms. Others undoubtedly can offer additional
suggestions on improving these and other designs.
Despite the shortcomings mentioned above, this
manual serves its purpose rather well. The manager
or osprey enthusiast is offered a series of designs that
are appropriate for many different local conditions.
Anyone contemplating construction and installation
of artificial nest structures, or facing problems aris-
ing from conflicts between ospreys and utility lines,
will profit from consulting this manual. — Sergej
Postupalsky, 1817 Simpson, Apartment 201,
Madison, WI 53713 U.S.A.

Literature Cited

Abbott, G.G. 1911. The home life of the osprey. With-
erby & Co., London, U.K.

Martin, C.O., W.A. Mitchell and D.A. Hammer.
1986. Osprey nest platforms. Rep. EL-86-21. U.S.
Army Corps Engineers, Vicksburg, MS U.S.A.
Postupalsky, S. and S.M. Stackpole. 1974. Artificial
nesting platforms for ospreys in Michigan. Pages 105-
117 in F.N. Hamerstrom, Jr., B.E. Harrell and R.R.
Olendorff [Eds.], Management of raptors. Raptor Res.
Rep. No. 2, Raptor Res. Found., Vermillion, SD U.S.A.

J. Raptor Res. 30(1):56

Manuscript Referees

The following people reviewed manuscripts for the Journal of Raptor Research in 1995. Peer review plays a vital
role in the publishing process and in improving the quality of the journal. The names of individuals who reviewed
two or more papers are followed with an asterisk.

Peter A. Abrams, John Alcock, Dean Amadon, David E. Andersen, Thomas G. Balgooyen, Marc J. Bechard,*
Dale Becker, James C. Bednarz, Isabelle Bellocq, Keith I. Bildstein,* David M. Bird, Hal Black, Peter H. Bloom,*
Lawrence J. Blus,* Gary R. Bortolotti,* Reed Bowman, Mark Boyce, Mike Britten, Serge Brodeur, Bryan T. Brown,
Joseph B. Buchanan, Evelyn Bull, Javier Bustamante,* Tom Cade, Richard J. Cannings, Susan Chaplin, Felipe
Chavez-Ramirez, Richard J. Clark, William S. Clark,* Tim H. Craig, Erica H. Craig, Cole Crocker-Bedford, Christine
Mitchell Custer, Dick Dekker,* Juan A. Donazar, Ronald D. Drobney, Gary Duke,* Jack Clinton Eitniear, David
H. Ellis,* James H. Enderson,* Sidney England, Paula Enriquez-Rocha, David Evans, Peter S. Ewin, K.M Exo,
John A. Faaborg, Sue E. Fairbanks, Joseph L. Ganey, Kathryn Grandison, Richard Griffiths, Teryl G. Grub, Ralph
J. Gutierrez, John Hagan, Ed Henckel, Charles J. Henny,* Steven Hoffman, Denver Holt,* Stuart Houston, Christine
Hubert, Ronald Jackman, Jerome Jackson, Fabian M. Jaksic,* Paul C. James, Jaime E. Jimenez, Paul Keim, Patricia
L. Kennedy, Paul Kerlinger, Ellen Ketterson, Jack S. Kirkley, Michael N. Kochert,* Erkki Korpimaki,* David Ligon,
Jeffrey Lincer, Carroll D. Littlefield, William S. Longlund, Jon Longmire, Santi Manosa, Jeffrey S. Marks,* John
Marzluff, D, Archibald McCallum,* Peter McLean, Heimo Mikkola, Thomas E. Morrell, Robert K. Murphy, Juan
Negro, R. Wayne Nelson, Thomas H. Nichols, Barry Noon, Lynn Oliphant,* Ralph S. Palmer, Alan F. Poole,* Kim
Poole, Sergej Postupalsky,* Charles R. Preston,* Patrick Redig,* Marco Restani,* Richard T. Reynolds,* Carlos
Martinez del Rio, Robert W. Risebrough, Robert N. Rosenfield, Philip F. Schempf, Marsha A. Schlee, Josef K.
Schmutz, Janis K.D. Seegar, Steve K. Sherrod, John A. Smallwood, Michael Smallwood, Dwight G. Smith, Noel
Snyder, Geir A. Sonerud, Mark V. Stalmaster, Karen S. Steenhof,* Jean-Claude Thibault, Helen Ulmshneider, Daniel
E. Varland, Andrew Village, F. Prescott Ward, Gary White, Clayton M. White,* Karen Wiebe, Stanley N. Wiemeyer,
Sanford R. Wilbur, David W. Wiley, James M. Willey, Neil D. Woffinden, Petra B. Wood, Brian Woodbridge, Glen
Woolfenden, Veta Wright.

THE RAPTOR RESEARCH EOUNDATION, INC.

(Founded 1966)

OFFICERS

PRESIDENT: David M. Bird SECRETARY: Betsy Hancock

VICE-PRESIDENT: Michael N. Kochert TREASURER: Jim Fitzpatrick

BOARD OF DIRECTORS

EASTERN DIRECTOR: Brian A. Millsap
CENTRAL DIRECTOR: Robert N. Rosenfield
MOUNTAIN & PACIFIC DIRECTOR:

Karen Steenhof

CANADIAN DIRECTOR: Gordon S. Court
INTERNATIONAL DIRECTOR #1:

Jemima ParryJones

INTERNATIONAL DIRECTOR #2:

Michael McGrady

DIRECTOR AT LARGE #1: Patricia L. Kennedy
DIRECTOR AT LARGE #2: John A. Smau wood
DIRECTOR AT LARGE #3: Keith L. Bildstein
DIRECTOR AT LARGE #4: CfiSAR MARQUEZ
DIRECTOR AT LARGE #5: Petra Bohall Wood
DIRECTOR AT LARGE #6: Katherine McKeever

EDITORIAL STAFF

OUT-GOING JOURNAL EDITOR: Carl D. Marti, Department of Zoology, Weber State University,

Ogden, UT 84408-2505 U.S.A.

IN-COMING JOURNAL EDITOR: MarcJ. Bechard, Department of Biology, Boise State University, Boise,

ID 83725 U.SA.

ASSOCIATE EDITORS

Keith L. Bildstein Fabian Jaksic

Gary R. Bortolotti Daniel E. Varland

Charles J. Henny Javier Bustamente

BOOK REVIEW EDITOR: Jeffrey S. Marks, Montana Cooperative Research Unit, University of Montana,

Missoula, MT 59812 U.S.A

EDITOR OF RRF KETTLE: Richard J. Clark

The Journal of Raptor Research is distributed quarterly to all current members. Original manuscripts
dealing with the biology and conservation of diurnal and nocturnal birds of prey are welcomed from
throughout the world, but must be written in English. Submissions can be in the form of research articles,
letters to the editor, thesis abstracts and book reviews. Contributors should submit a typewritten original
and three copies to the Editor. All submissions must be typewritten and double-spaced on one side of 216
X 278 mm (SVz X 11 in.) or standard international, white, bond paper, with 25 mm (1 in.) margins. The
cover page should contain a title, the author’s full name(s) and address(es). Name and address should be
centered on the cover page. If the current address is different, indicate this via a footnote. A short version
of the title, not exceeding 35 characters, should be provided for a running head. An abstract of about
250 words should accompany all research articles on a separate page.

Tables, one to a page, should be double-spaced throughout and be assigned consecutive Arabic numer-
als. Collect all figure legends on a separate page. Each illustration should be centered on a single page
and be no smaller than final size and no larger than twice final size. The name of the author (s) and figure
number, assigned consecutively using Arabic numerals, should be pencilled on tbe back of each figure.

Names for birds should follow the A.O.U. Checklist of North American Birds (6th ed., 1983) or another
authoritative source for other regions. Subspecific identification should be cited only when pertinent to
the material presented. Metric units should be used for all measurements. Use the 24-hour clock (e.g.,
0830 H and 2030 H) and “continental” dating (e.g., 1 January 1990).

Refer to a recent issue of the journal for details in format. Explicit instructions and publication policy
are outlined in “Information for contributors,”/. Raptor Res., Vol. 27(4), and are available from the
editor.

1996 ANNUAL MEETING

The Raptor Research Foundation, Inc. 1996 annual meeting will be held jointly with the American
Ornithologists’ Union annual meeting on 13-17 August at Boise State University, Boise, Idaho.
Details about the meeting and a call for papers will be mailed to Foundation members in the spring
of 1996 and can be obtained from Peter Lowther, Scientific Program Chairman, Field Museum of
Natural History, Roosevelt Road at Lakeshore Drive, Chicago, IL 60605-2496, (telephone 312 922-
9410 ext. 461; Fax 312 922-2572; e-mail lowther@fmnh.org) and Marc Bechard and Alfred Dufty,
Local Co-chairs, Department of Biology, Boise State University, Boise, ID 83725 (telephone 208 385-
3262; Fax 208 385-3006; e-mail rbibecha@idbsu.idbsu.edu or adufty@claven.idbsu.edu).

Raptor Research Foundation, Inc., Awards
Recognition for Significant Contributions^

The Dean Amadon Award recognizes an individual who has made significant contributions in the field of
systematics or distribution of raptors. Contact: Dr. Clayton White, 161 WIDE, Department of Zoology,
Brigham Young University, Provo, UT 84602 U.SA. Deadline August 15.

The Tom Cade Award recognizes an individual who has made significant advances in the area of captive
propagation and reintroduction of raptors. Contact: Dr. Brian Walton, Predatory Bird Research Group,
Lower Quarry, University of California, Santa Cruz, CA 95064 U.SA. Deadline: August 15.

The Fran and Frederick Hamerstrom Award recognizes an individual who has contributed significantly to the
understanding of raptor ecology and natural history. Contact: Dr. David E. Andersen, Department of
Fisheries and Wildlife, 200 Hodson HaU, 1980 FolweU Avenue, University of Minnesota, St. Paul, MN
55108 U.S.A. Deadline: August 15.

Recognition and Travel Assistance

The James R. Koplin Travel Award is given to a student who is the senior author of the paper to be presented
at the meeting for which travel funds are requested. Contact: Dr. Petra Wood, West Virginia Cooperative
Fish and Wildlife Research Unit, P.O. Box 6125, Percival Hall, Room 333, Morgantown, WV 26506-6125
U.S.A. Deadline: established for conference paper abstracts.

The William C. Andersen Memorial Award is given to the student who presents the best paper at the annual
Raptor Research Foundation Meeting. Contact: Ms. Laurie Goodrich, Hawk Mountain Sanctuary, Rural
Route 2, Box 191, Kempton, PA 19529-9449 U.SA. Deadline: Deadline established for meeting paper
abstracts.

Grants^

The Stephen R. Tully Memorial Grant for $500 is given to support research, management and conservation
of raptors, especially to students and amateurs with limited access to alternative funding. Contact: Alan
Jenkins, George Miksch Sutton Avian Research Center, Inc., P.O. Box 2007, Bartlesville, OK 74005-2007
U.SA, Deadline: September 10.

The Leslie Brown Memorial Grant for $500-$!, 000 is given to support research and/or the dissemination of
information on raptors, especially to individuals carrying out work in Africa. Contact: Dr. Jeffrey L. Lincer,
Sweetwater Environmental Biologists, Inc., 3838 Camino del Rio North, Suite 270, San Diego, CA 92108
U.S.A. Deadline: September 15.

^ Nominations should include: (1) the name, title and address of both nominee and nominator, (2) the names
of three persons qualified to evaluate the nominee’s scientific contribution, (3) a brief (one page) summary
of the scientific contribution of the nominee.

^ Send 5 copies of a proposal (^5 pages) describing tbe applicant’s background, study goals and methods,
anticipated budget, and other funding.

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